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6.8SPC FAQ (Page 3 of 3)
| It will depend largely on what exactly the threads are on the barrel you have or are getting. I have 5/8-24 hreads on my threaded barrel so I have a .308 phantom. Some barrels have/had 9/16 hread so 9mm FH's were used. I do not recommend a 1/2-28 thread because of the reduced muzzle diameter. It is best to go with the 5/8 thread and use the .308 FH's for the best selection. I also believe this is becoming the standard for 6.8. |
I'll be getting a Ko-tonics upper, so I think they are 5/8-24 thread. At least I know what kind to search for now. |
Tempus fugit. Frater, memento mori.
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The short answer to your two questions is...yes. However, the limiting factor in the AR is the magazine. You are limited to a COAL of 2.26"-2.27" with the C-Products magazines and ~ 2.31" with the PRI magazines. You cannot get about this, so #1 would be more applicable here. |
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Actually this is where programs like QuickLoad come in real handy because you can see what gives you more in relation to pressure. In most cases you will get more velocity by increasing the OAL and using more powder then keeping OAL super short and having more run up. But again twist plays into this you can't simply forget about it. But heres an example. an 1:11 twist SPCII chamber will get greater velocity by increasing the OAL of the round to the max for magazine or until you are no closer then .020 to the lands and adding in more powder then to have less powder and keep the throat longer and having it jump to the lands. It wil also get you better accuracy with most rounds. Now when you start using less then ideal twist like the 1:10 and the SPCII there is this line you have to dance between the two. Then it will be a crap shoot. There won't be enough of a difference between going long or short. As you can get up to max pressure either way and the velocity won't be much different. Now if you kep the same powder charge and increase the OAL you will have lower pressure and slightly less velocity. If you have a charge that is at the edge and you decrease the OAL it is not going to get you more velocity without the pressure jsut becasue of the longer leade. You will most likely be over pressure. This again has to do with the twist it ahs to deal with. Its not easier to answer and harder to explain properly. I hope I helped more then I confused things. Tim Tim Tim |
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When Size Matters 6.8 SPC
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When Size Matters 6.8 SPC
I run 2.285 COAL in my C-Products mags with a little room to spare |
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hanks you are right I wrote CP with the length i run my OAL in and with PRI I wrote the actual space of the smallest on I measured. Your measurement are in line with mine. Sorry about that. Tim |
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A suggestion for all
1> Do your Homework 
2> Ask lots of Questions 
tim of ko-tonics and art from SSA are the experts in this field- they have driven the 6.8 bus to where it is. 3>BE CAREFUL  Safety, especially when handloading heat needs to be respected.
BEFORE YOU SPEND A DIME-READ-READ-READ F.Y.I 18" Ko-Tonics Upper with YHM Lt-wt quad rail + Sun Devil Lower Billet + Jp 3.5 Trigger + Olumpic AC-4 hydraulic recoil buffer + 10x Bushnell 3200 scope =Equals= ONE RAGGED HOLE at 100 Yards[:o)] |
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Tackdriver, I tried the buffer and it was a no go for hand loading. With light loads it seemed OK then I started having all kinds of issues. It would through a case perfect 6 ft @ 4:30 and then the next would barely fall out the one would jam and on and on. I even tried my old basic test load of 29.5 H322 110 Pro Hunter @ 2.27 and it would not hold the bolt back it would just catch the carrier. It was very erratic. I am thinking maybe it was actually bouncing off the bottom to fast or something weird. I switched to an extra power SSS Flat CS wire Spring and standard rifle buffer and it was 100% even with the finicky hrdy stuff. It may work better with a 1:11 or faster twist. I wish it had worked I really like the concept and getting rid of the spring. I think it would have to be adjustable like they use to have for it to work. Now that I am sure it was the buffer and the regular one is working I will switch to the Enidine hydraulic buffer I also have. I bet that will turn out to be the best of all. I love the balance with the PRS stock and the 18" barrel setup. Recoil and movement is very low. I am using a 1:12 Pac-Nor Harrison of AR15Performance finished for me. I am getting very very good performance. I think 1:12 is the ideal for the 6.8 in an AR and a 1:11 is right for bolt guns. Right now I got the following on the first day or two of testing. 18" 1:12 DMR 6 groove I think 3 would be ideal 90 TNT 3200 fps very light swipes 3150 fps clean 110 TSX 2800 fps clean and can get more. I think 2900 or more 130 speer 2575 fps clean but was using 3031 and its took bulky but has a great profile otherwise With AA 2520 or BL-C2 or 10x I should be well over 2600 Looking aback over all the data I have collected each inch of twist is worth 75-100 of velocity. I also got 2695 from the old Hrdy V-max factory load The KT 20" got 2620 so 2" shorter and more vel. I am happy. It was getting 3/8" groups when Harrison was function testing it. You will only see 1:12 on my guns from now on if I pick the barrel. |
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Well im using a 1-11 barrel and the buffer seems to be consistent-all the cases land in a 1-foot circle with a little variation in the landing zone between different loads. i'm using benchmark powder, br-4 primers and anywhere from 24 grains to 28 grains in a charge with no pressure signs like flattened primers. i don't have any explanation for the variety you're experiencing from one shot to the next. if the loads are equal than the operating forces in the weapon shouldn't change from one shot to the next.How many rounds has your buffer seen? if the buffer is weak that might explain it. The only other thing I can think is if theres a leak or blockage in the gas system or something else causing the operation to change from one shot to another. I still haven't gotten the right loads for the 120 barnes solids-sometimes 4-6 inches between impact at 100 yds. 130 gr noslers aren't much better- those are still getting 1.5-2.5" groups at 100 yards. since theres no published max loads for the 130 grain bullets im being really careful working the loads up, going 0.1 grains at a time, 5 rounds at each group. and carefully inspecting cases and primers after each shot.if you want to shoot me an email, ill give you the exact charges in private. =How well does the 1-12 group the standard 115 gr otm loads from SSA? What about the 130gr class? Any thought on the minimum twist for 130's? -Being longer they (the 1.295" barnes and 1.13" nosler SP's) would logically need faster twist to stabilize the bullet (as compared to 115gr SMK that measures 0.955). Since the 120 barnes banded solid is so much longer-longer than even the 130 grain bullets that might explain the erratic groups im gettting. any thoughts? Also the barnes projectiles are so long that i have to seat very deep to keep the 2.260 OAL for the AR action. I' think they may be too long but might work wonderful in a bolt gun loaded to some like 2.35 or even out to maybe as far as a 2.6'' OAL. |
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With the Barnes 120s try Rel 10x or H335. The real issue you are going to have with accuracy is that those dang bullets are just way to long. The bullet neck is inside the case and that is what is most likely causing your accuracy issues. You really should hop over to 68forums.com and speak with Constructor he has done the most testing with the 120s and does considerable amount of competing. On the 130s I am going to be trying a few powder that have not been tried as of yet. I might suggest you give Hodgdon BL-C2 a try. It is a bit slower then H335 and almost as dense. If this other powder works out I will post my results. I am wanting a solid 2600 with 1 moa accuracy. That will make it a very good hunting load and with 3even a light load of just under 2500 will make MPF for three gun comp. I know of 4-5 bullet and loads that make MPF. One thing to try with the 120 barnes. Trim the necks on the case as short as possible to see if you can get the Ogive out of the case. The closer you get he less erratic your groups will be. In the 130s you need to say as short as possible that leaves you witht he Speer SP and SPBT the Sierra 130 SP and SPBC. The Speers ahve the best BC and are the shortest. If you have the longer leade chamber SPCII I think you can load them all the way out to 2.29 but please confirm it for your self. We sue to think we could only go 2.26 as they are so blunt but I was playing with them a few daysa a go and went all the way to 2.305 without having any engraving marks so I am thinking we may have been wrong. I wish I hadn't crushed my case that went to the Hrdy OAL gauge set or I would know with 100% certainty. Hope some of this helps |
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When Size Matters 6.8 SPC
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I went and visited the range on sunday am and i think i found the right load for the 120's.finally got 4 rounds in under 2 inches and the first three were just over an inch. i think trimming the cases down a little extra will do the rest.If i can make them accurate, the 120's may end up being the best long range bullet for tactical applications, the increased muzzle vel from the bands and the longer profile should give a significant range improvement, maybe 50 to 75 yards, and being one solid metal it should do a better job punching through light brush that would normally cause rapid fragmentation at high velocities like with standard 5.56mm nato rounds. I also got lucky with the 300 win mag load.first four shot group was under 2 inches with 3 under 1", and the other 4 loads got progressively worse, although some of that may be a result of the pounding of 25 rounds in lightweight rifle and near maximum magnum loads......hisH335 the 120gr best group http://www.tool-tees.com/IMAGE/0005.jpg |
| If you haven't shot it over a chron yet be prepared to be disappointed the BenchMark even thou it looks to be good is not a great performer in the 6.8 for vel. With the 120s loaded to 2.30 and try using REL 10x, X-term, Norma 200 is very good but doubt you have that local. H335 or H322 any of these will be better the Bench Mark. For whatever reason BenchMark just has not worked well for a single person that has tried it. Believe me when I say we were all disappointed. With the 120s you should be close to 1 moa with a good load. Work up to you see swipe or other sign and back of a 1/2 grain you know the drill. |
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When Size Matters 6.8 SPC
Tackdriver We looked at the 120 Barnes but could not get the accuracy we wanted from it. God knows if we were to load and sell it we would have gotten slammed by someone. The 120 grain barnes requires more velocity like from a 270 because of its length to get dime size groups. The groups you got were about the best you can do. Art- SSA |
Yep even though it seems to stabilize in the 11 twist it is right on the ragged edge and gives erratic results at the velocity most can push them. One of the signs you need more spin is with groups that open up or get flyers with different weather or temps. When Constructor got them up to 2700 they did OK but again he had to trim the cases befoer they settled down. That bullet is 1.248 so when you consider the max for ideal powder is under 1.1 this is really to long. But if you only need 1.5 moa if may work for you. I would still shorten the cases to make sure that neck ogive junction is outside the case neck and then shoot 6-10 groups on a few different days and make your decision. If you are using a 10 twist that is what is needed as that is plenty of twist or the length. Constructor has told me many times that if the neck of the bullet is inside the neck of the case you will get groups that will have flyers. Depending what you consider your max range look at the Speer 130 Hot Cor SPBT it has a BC of .448 IIRC and I have been able to push them to just under 2600 from an 18"and the 130 SP to just over 2600. You could take a look at the new Barnes TTSX with its BC of .377 and has the same bands so you can drive them over 2700. That will keep you super sonic past 800. To fit the AR mag limit of 1.1" bullet and also weight the best you are are going to do with a Tangent bullet is under .400 with a secant bullet you can get into the .400 but then you have to work to get a good load. It is doable its just not as easy as with a tangent bullet. I would try loading them longer and single load them to see if you can get te accuracy that way. As if you can or can't you will know if they are worth trimiming the cases down. |
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When Size Matters 6.8 SPC
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When Size Matters 6.8 SPC
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Originally Posted By Carlp336:
where can i buy a 20" + 6.8 barrel im not seeing any that arent custom builds is that the case ? I know of no readily available 20" plus barrels. Mostly because it doesn't give much velocity advantage. The 6.8 was designed with shorter barrel lengths in mind. For what you are looking for 18"-20" should be your best bet. I have both a 16" and a 20" and only see about 150 fps difference between the 2 lengths. After a certain point it becomes less productive due to the small case capacity. |
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Wow, this was great. I took the last hour and read this entire thread..learned more about chamber/bullet/barrel relationships and dynamics than I could have ever asked. Thanks. The 6.8 SPC sure is an impressive round, but I have a couple of questions if I may. If all hell breaks loose and we find ourselves in a civil defense circumstance, which round would you rather count on, the 6.8 or the 5.56? My question is based mostly on ammo availability. Would a guy be smart to have a 6.8 as his primary high tech small tactical weapon with a more generic 5.56 as a back-up, or would you be comfortable staying soley with the 6.8? I see myself building a high quality (KoTonics or equiv)6.8, and then something like an inexpensive (Stag 2H or 2HT) 5.56 as a back up.
Any thoughts? (Also doing a custom AR10 for "reaching out") Second question, where is a good place to buy bulk 6.8 ammo, and what cartridge would be a good recommendation for this described scenario? Thanks in advance. |
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Originally Posted By steelcomp:
Wow, this was great. I took the last hour and read this entire thread..learned more about chamber/bullet/barrel relationships and dynamics than I could have ever asked. Thanks. The 6.8 SPC sure is an impressive round, but I have a couple of questions if I may. If all hell breaks loose and we find ourselves in a civil defense circumstance, which round would you rather count on, the 6.8 or the 5.56? My question is based mostly on ammo availability. Would a guy be smart to have a 6.8 as his primary high tech small tactical weapon with a more generic 5.56 as a back-up, or would you be comfortable staying soley with the 6.8? I see myself building a high quality (KoTonics or equiv)6.8, and then something like an inexpensive (Stag 2H or 2HT) 5.56 as a back up. Any thoughts? (Also doing a custom AR10 for "reaching out") Second question, where is a good place to buy bulk 6.8 ammo, and what cartridge would be a good recommendation for this described scenario? Thanks in advance. Question #1: I think you answered your own question. Own both. I do, for the very reasons you stated. You could also own two uppers with the appropriate mags. Question #2: I not aware of bulk 6.8 ammo but that doesn't mean it doesn't exist. Sellier & Bellot just introduced their 6.8 SPC cartridge but I don't have first hand knowledge of price or quality of product. If you want a 6.8 I strongly suggest you start reloading if you currently aren't. That way you get the best performance out of whatever bullet that suits your mission & barrel. As far as bullet selection is concerned, you should read this. That forum is another good source of info regarding the 6.8 mm SPC cartridge. Jeff |
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Originally Posted By river_rat:
Originally Posted By Carlp336:
where can i buy a 20" + 6.8 barrel im not seeing any that arent custom builds is that the case ? I know of no readily available 20" plus barrels. Mostly because it doesn't give much velocity advantage. The 6.8 was designed with shorter barrel lengths in mind. For what you are looking for 18"-20" should be your best bet. I have both a 16" and a 20" and only see about 150 fps difference between the 2 lengths. After a certain point it becomes less productive due to the small case capacity. River Rat, Just curious where you found your 20" barrel? |
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Originally Posted By steelcomp:
. If all hell breaks loose and we find ourselves in a civil defense circumstance, which round would you rather count on, the 6.8 or the 5.56? While I have both, I'd probably 'count on' my 6.8 more. After reading ShaneS's experience in the Katrina aftermath (see the Survial Forum in the Outdoors area) I want a round that will do really well after penetrating a car door or auto glass. For that job the 6.8 is head and shoulders above the 5.56. My question is based mostly on ammo availability.
I used to think like that. But I've since thought about it some more after reading AARs from various disaster survivors. Things you can count on if civil unrest occurs. 1. Going to the shopping areas during civil unrest is a BAAAD idea (see Reginald Denny) 2. Assuming you make it to the store you'll find the Govt QUICKLY stops the sale of guns and ammo when they see unrest. 3. Then assuming you get to the store before the Govt has shut down the sale of arms & ammo you'll find the stores will be out of ammo in whatever caliber you need (it goes really quick). Which means you need to have your ammo alaready onhand well BEFORE the event. So in my mind it matters not if Walmart carries the ammo I intend to shoot. Stock up beforehand via intertnet/mail (like with SSA) and/or roll your own. Would a guy be smart to have a 6.8 as his primary high tech small tactical weapon with a more generic 5.56 as a back-up,
I think so (heck that's what I'm doing). If nothing else the 5.56 makes for a cheaper way to train if you have it in the same setup as your 6.8. or would you be comfortable staying soley with the 6.8?
I'd have no problem with this, assuming I'm only providing weapons/ammo for myself and I'm not 'hooking up' with others. If your plan includes hooking up with your buddies you might want to consider having the same caliber and weapon type. Any thoughts? (Also doing a custom AR10 for "reaching out")
A nice 18" or 20" 6.8 upper with a free floated barrel does a nice job of 'reaching out' for realistic ranges and you can use the same ammo & magazines. Second question, where is a good place to buy bulk 6.8 ammo, and what cartridge would be a good recommendation for this described scenario?
SSA their 'Combat' 115gr OTM. Not cheap but you can buy it in 'bulk'. My choice for long range shooting so far has been the 110gr VMAX. It's given me good accuracy and has a higher BC and velocity than the 115gr OTM. |
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Link to 6.8 SPC performance test report, posted here on ARFCOM
http://www.ar15.com/forums/topic.html?b=3&f=121&t=369145 |
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Originally Posted By carbinero:
Seems like this oughta be a sticky... Umm it is. Did you look in the FAQ thread stickied at the top? |
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"All Arfcommers should wear thier multicam smoking jackets or jammies around the house in anticipation of JBT tasering/dog shooting/civil rights violation or the occasional impromptu gangbanger street theater." - m24sh
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Originally Posted By MAJC:
Originally Posted By Forest Umm it is. Did you look in the FAQ thread stickied at the top? Not any more- it's seven topics down the page and no "thumbtack". Check the TACKED FAQ thread. You'll find a link to THIS thread is tacked there. So it's still tacked, just taking up less space at the top of the forum. |
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"All Arfcommers should wear thier multicam smoking jackets or jammies around the house in anticipation of JBT tasering/dog shooting/civil rights violation or the occasional impromptu gangbanger street theater." - m24sh
"All Arfcommers should wear thier multicam smoking jackets or jammies around the house in anticipation of JBT tasering/dog shooting/civil rights violation or the occasional impromptu gangbanger street theater." - m24sh
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Originally Posted By Silver78:
OK - so it's referred to in the tacked thread - but won't it need bumping to keep from falling into the archive? Nope the new system allows for threads that will not be archived so they can stay active. |
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"All Arfcommers should wear thier multicam smoking jackets or jammies around the house in anticipation of JBT tasering/dog shooting/civil rights violation or the occasional impromptu gangbanger street theater." - m24sh
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Originally Posted By paulosantos:
Originally Posted By mustang_52:
Has Stags 6.8 rifles always been improved sammi? I bought a 6.8 upper the end of last year from them and I am wondering if I can handle the hotter loads? When I recently called up and asked, the guy told me he "thinks" it is the improved chamber because they had talked about it and supposedly had changed it. If I were you, I would call and get a straight answer from them. If not, you can always buy some combat rounds and check for pressure signs. As I was in on the group buy on the Stag kits, not knowing I could have gotten a 6.8, I saw where people were reporting they were getting bbls marked 1/11 twist. I contacted STAG and despite their web info, ( which states 1/10"), all NEW bbls are 4 groove, 1/11" with the SAMMI II "improved" chamber. Wished I'd known this before ordering another 5.56 Kit. After reading an article on SSA's ammo, I was going to wait until the specs were brought up to speed. Damn, I wished I knew this at the time. I'd trade a 5.56 upper for a 6.8 if someone is interested. I should get my new kit within the next two weeks. I already have 5 6.8 mags just waiting for that damn expensive ammo...........This is their response: Jon, We are using the SAAMI SPECII chamber on all of our firearms along with 4 groove 1:11 twist. If you have any further questions please contact us again. David Larson Stag Arms, LLC 860-229-9994 x225 www.stagarms.com |
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This is a great thread, and I've tried to read as much as I can digest. I have a question that I just can't find an answer that I'm sure I'm reading 100% right, so if someone can help give me a straight answer, It'd be great.
I'm getting ready to build my first rifle on the AR platform (heck, my first full build, period) and I want to build it in 6.8. My question is, can I buy a basic, striped or not, A4 upper, say a basic Stag A4 and put a 6.8 BCG in it, or do I need to look for a upper that is specifically marked/made for the 6.8? I know I can put it on a basic AR-15 LOWER, but what about the basic UPPER? Thanks in advance, and sorry if this answer is somewhere I should have already found it. |
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After reading ShaneS's experience in the Katrina aftermath (see the Survial Forum in the Outdoors area) I want a round that will do really well after penetrating a car door or auto glass.
linky PLZ! 
I cannot find this thread in the forum, but I really want to read.  (I've tried multiple searches here, and google.  )
I'm on a DIY multi-Cal AR lower build. The 6.8 has caught my interest. I was leaning 5.56/.223/wylde barrel, but only for the "my neighbor may have the same ammo/config/setup" when talking SHTF. This DIY build is not meant for primary HD, as I already have that covered with a Glock 22, and Winchester SX2 Practical MKII. I am looking for something more 100+yds CQB. A 5.56/.223 build will fulfill, but a true life SHTF perspective may encourage me to invest in the 6.8 (with a .223/5.56 complete upper in the background). |
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Originally Posted By 00Ghost00: After reading ShaneS's experience in the Katrina aftermath (see the Survial Forum in the Outdoors area) I want a round that will do really well after penetrating a car door or auto glass. linky PLZ! I cannot find this thread in the forum, but I really want to read. (I've tried multiple searches here, and google. )Sorry by now it's in the Archives and only Team Members can view it. http://www.ar15.com/archive/topic.html?b=10&f=17&t=606652 |
'98 Jeep XJ Owner
6.8 > 6.5
6.8 > 6.5
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For 130 gr I'm digging the Sierra gamekings, others have sworn by the Noslers, but I can't find them around here. There are recipies for the 130s in the 6.8 Reloading FAQ in the 6.8 FAQ thread posted in the FAQ page at the top of this forum. |
'98 Jeep XJ Owner
6.8 > 6.5
6.8 > 6.5
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Originally Posted By Forest: Originally Posted By 00Ghost00: After reading ShaneS's experience in the Katrina aftermath (see the Survial Forum in the Outdoors area) I want a round that will do really well after penetrating a car door or auto glass. linky PLZ! I cannot find this thread in the forum, but I really want to read. (I've tried multiple searches here, and google. )Sorry by now it's in the Archives and only Team Members can view it. http://www.ar15.com/archive/topic.html?b=10&f=17&t=606652 Been reading forever thanks to you..  |
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per the request in another 68 chamber thread:
here is a quote from Harrison at AR Performance: Chamber discussion
Default 6.8 chambers- SAAMI, SPCII, DMR, 6.8x43, Noveske Mod 1 There have been lots of threads about this lately for some reason so I'll try to explain it. Formal names first, slang after. (2004)Remington 6.8x43 SPC-(SAAMI)- has a .050 freebore and when submitted to SAAMI had the correct 45 degree cone angle, has a .278 diameter freebore. Some drawings from PTG has a 80 degree cone angle, no one knows where the error originated. (Jan 2006)6.8 Remington SPCII-(SPCII)- had a .100 freebore originally drawn by Art of SSA or Barrett not known for sure had the correct 45 degree cone angle, has a .278 diameter freebore, .3085 neck. Some drawings from PTG has a 80 degree cone angle. (2007)6.8x43 DMR (DMR)- has a .095 freebore, .277 dia and a .305 neck diameter it was designed to correct the bad 80 degree cone angle and be a little more accurate in stainless match barrels because of the shorter freebore and .277 dia leade. Only used in ARP stainless match barrels. (2008) DMR-C enlarged only enough to take into account the thickness of the chrome in the chamber, neck .0307/.3075-Used only in the chrome lined barrels we had produce in late 2008 and sold in early 2009 (2009) 6.8x43- has a .095 freebore, .2775 dia with the correct 45 degree cone angle and a .3085/.309 neck. A call came in one day which I missed so they called Tim_W, they said they were planning to submit a new drawing to SAAMI with the help of either Rem or Hornady to get the better spec chamber approved by SAAMI. They said they were planning on submitting the SPCII but wanted our input since we had tested the chambers more than anyone. Tim and I talked about what would be best for a true combat chamber, not a hunting or match chamber. We added a very small amount of taper in the neck and body to aid extraction, the freebore was increased to .2775 from what the DMR chamber had, The neck dia was increased to .3085/.309 taper. We guessed if the mil would adopt the cartridge they would call it the 6.8x43 Nato so we just dropped the "Remington" and "SPC" from the name and Tim sent it back to the person that called noting these would be our recommended changes. Of course nothing happened with SAAMI but that is how the 6.8x43 that I presently use came about. Noveske mod 1-no real idea, they say it has a .100 freebore. (2010) New SPCII- Ben with Bison posted a new SPCII drawing that shows a .114 long freebore with .278 diameter and the correct 45 degree cone angle, everything else is the same as the other SPCII. IMO all of these chambers except the original "Remington 6.8x43 SPC"(SAAMI) will handle high performance ammo. These chambers seem to confuse many possibly because the public has been exposed to the chambers and given more info than what has been released about the 5.56 and 308 chambers. There are 14 308 chambers that I know about but most of the public thinks there are only 2 the 308 and the 7.62x51 nato. There are at least 10 223/.556 chambers that I know of, the 6.8 isn't different it is just that there is a lot more info being passed around to the public about it. |
6.8SPC FAQ (Page 3 of 3)
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