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Posted: 11/20/2007 12:35:38 PM EDT
This is Hornady TAP 75gr OTM fired through my 10.5" SBR at 25 yards. Based on the pics below of the bullet holes would it be OK to fire this ammo from this rifle through a suppressor? (HALO) They look pretty stable to me.
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Posted: 11/20/2007 2:08:03 PM EDT
[#1]
Gemtech warns against heavy boat tail bullets from short barrels with not fast enough twist, any instability won't show up till the silencer is on and the asymetrical gasses push sideways on the boat tail portion of the bullet as it passes through the baffle.
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Posted: 11/20/2007 2:56:52 PM EDT
[#2]
What is the length of the bullet?It's not the wieght but the length.Ill have too look for my link to a site where you type in caliber and twist and it will tell you max. length you can use for stability,or just go with the manufacturers recommendation.
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Posted: 11/20/2007 4:37:28 PM EDT
[#3]
It's a Hornady 75 gr OTM. No idea how long it is, I never pulled one and don't really want to.
The barrel is a 1:9. I know some 1:9 will shoot the heavy/longer bullet and others, maybe not. My main concern was the effect of a suppressor on the round which Tommyboy addressed. However a twist that is not fast enough could be 1:9.5 or 1:12 which would definitely be to slow. Hopefully Gemtech will be along shortly and say either you can probably get away with it since it didn't keyhole that plate. Or don't do it use only a 1:7 twist. |
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Posted: 11/20/2007 4:45:53 PM EDT
[#4]
I dont know why you want to tempt fate. You are on the low end of barrel length for suppressor use, and you are on the high end of bullet weight for 1:9 twist. Seems like high potential for disaster.
I would expect a tighter group with that ammo at that range. |
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Posted: 11/20/2007 4:59:22 PM EDT
[#5]
I had no intention to shoot one ragged hole. I wanted the shots spread out so I could look at the holes, and show them to all of you.
 Plenty of people use 10.5 barrels with 75 & 77 grain bullets and do so with a suppressor. The question is purely about stabilization. |
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Posted: 11/20/2007 5:34:12 PM EDT
[#6]
ah... I see you clarified later.
If you are going with two tax stamps don't be cheap. Replace the barrel with something a little better suited. JMHO |
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Posted: 11/20/2007 5:35:30 PM EDT
[#7]
Affirmative! |
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Posted: 11/21/2007 1:44:44 PM EDT
[#8]
Make the same test again but closer ,as close as you can without blowing the target away
Some bullets( actually all ) wobbles a bit at the start (leaving the barrel )but stabilize later It how they behave when they leaves the barrel whats count for the can  How they behave later is for precision Ps ,,next time ,,shoot a smiley 
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Posted: 11/21/2007 2:03:31 PM EDT
[#9]
If you want to use heavy loads from a 10.5" barrel + suppressor, get a 1:7. |
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Posted: 11/21/2007 5:03:59 PM EDT
[#10]
Well, today I ordered a CMMG 10.3 1:7 That ought to do it.
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Posted: 11/21/2007 6:43:14 PM EDT
[#11]
You do understand that your gun will be no quieter nor more powerful with 75s than it is with 55s and that the purpose of 75s is to carry the effective range out of match rifles to 600meters, not exactly the role of a 10" barrel.
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Posted: 11/21/2007 8:05:32 PM EDT
[#12]
That particular projectile, with enough pressure, makes a 10.5" gun a seriously badass defensive weapon out to defensive ranges. |
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Posted: 11/21/2007 8:54:40 PM EDT
[#13]
That is what I want. I guess with the 1:7 I can shoot any bullet that can be loaded to magazine length. |
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Posted: 11/21/2007 10:56:41 PM EDT
[#14]
Wait a sec, a LMT 10.5 with a 1x9 twist?
Is it just me or is that an odd bird? |
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Posted: 11/21/2007 11:00:06 PM EDT
[#15]
I don't see LMT's name in the thread until your post... 10.5 1:9, definitely not LMT. |
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Posted: 11/21/2007 11:07:44 PM EDT
[#16]
Woah, major brainfart.
In the first line of his post I see "SBR" and read "LMT". That's some damn good marketing folks. 
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Posted: 11/23/2007 8:46:01 PM EDT
[#17]
The purpose of 75's in short barrel guns is to enhance the effective fragmentation range. Where did that match rifle and 600 yard stuff come from? |
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Posted: 11/23/2007 8:46:20 PM EDT
[#18]
That's how I see it. |
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Posted: 11/26/2007 1:20:53 PM EDT
[#19]
the 60gr. v-max & 64gr. win p.p. both have more bearing surface than the hornady 75gr. hpbt. the hornady 75gr. stabilizes out of every 1/9 i've seen them shot through. ymmv
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Posted: 11/26/2007 1:26:32 PM EDT
[#20]
10.5" is the key here. Longer barrels have no problem with them.... but shorter ones can be iffy. If you didnt have a supressor - you wouldnt care about the potential for an occasional keyhole. With a supressor.... the risks are much higher. |
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Posted: 11/26/2007 5:23:32 PM EDT
[#21]
Don't you just love people who know exactly what they are talking about. |
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Posted: 11/27/2007 7:08:57 PM EDT
[#22]
I agree with that opinion very strongly. MitchTheWitch is spot on here. Listen to him. Mark |
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Posted: 11/27/2007 7:42:52 PM EDT
[#23]
Let's review. Heavier bullet, reduced volocity, short barrel, more reduced velocity, chance of expansion rather than over-penetration, not good. 55gr bullet faster velocity, better chance of stabilization, better chance of explosive expansion transferring it's energy to the target rather than punching right through. |
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Posted: 11/27/2007 7:56:10 PM EDT
[#24]
You couldn't be more wrong. First, it has nothing to do with energy transfer. It has to do with fragmentation creating a large enough permanent, and temporary cavity, to do the most damage to the central nervous system and vital organs. The new loads using 75gr OTM and 77gr SMK are being developed for shorter barrels, and under testing are able to demonstrate MUCH better fragmentation at even farther distances.... even at much lower velocities. Your data might be true for varmint rounds... but not for 12" if penetration in human tissue.
The "purpose" of 75's is multi faceted. Heavier bullets are used for all sorts of reasons. And in short barrels, they are used because they demonstrate much better fragmentation than M193 (55gr) and M855 (62gr), and allow for fragmentation to occur at longer distances where 55 and 62 bullets fail to fragment. Pay special attention to the fragmentation thresholds of the 75 and 77gr rounds.... they fragment at MUCH lower velocities which make them suitable for short barreled rifles: www.btammolabs.com/tests/5.htm www.btammolabs.com/tests/6.htm |
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Posted: 11/27/2007 8:16:32 PM EDT
[#25]
Damn Tommy... Open mouth, insert foot.
The speeds at which Mk262 and other heavy grain 5.56 rounds fly out of even short barrels like 10.5 or 7.5 inches isn't anywhere slow enough to cause them to destabilize. The "speed" you need to keep high is rotational speed governed by the twist rate. ETA: and yeah, the LMT and 10.5" is what caused me to question the 1:9 earlier... |
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Posted: 11/27/2007 8:32:55 PM EDT
[#26]
Those tests were 16" barrels, subtract 500fps from those figures and do it again, and they were comparing hollowpoint bullets to military ball, compare to lighter weight hollowpoint bullets.
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Posted: 11/28/2007 6:54:27 AM EDT
[#27]
I give up. |
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Posted: 11/28/2007 8:09:14 AM EDT
[#28]
The age old unsolved question of bullet weight and velocity and which is more effective.
Half the croud is going to Aguilla 60 bullets and saying better knockdown and half the croud goes to 17HM2 sqawking about flatter trajectory and explosive expansion. In the end the squirrel is dead in both situations. Then there is the 204 Ruger debate where somehow they think thier ammo is different than a .223 shooting a 40gr bullet. That being said your original question was about stability of a 75gr bullet in a shorth 1/9 twist barrel and I agree with general opinion that one should minimum step up to 1/7 twist barrel. |
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Posted: 11/28/2007 3:47:21 PM EDT
[#29]
Twist rate is not the only thing controlling the rotational speed. For any fixed twist rate the RPMs will be higher the higher the velocity is when it leaves the barrel. |
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Posted: 11/28/2007 4:38:47 PM EDT
[#30]
That's pretty much governed by twist rate- If you have two barrels, one at 1 in 9 and one at 1 in 7 and a 2700 fps bullet coming out of each, one will be rotating faster due to the twist.
That was my point and that's all my point was. Tommy- your English, spelling AND grammar are pretty awful. Sometimes I don't really know what you are talking about until I think about reality then I can fit your little puzzle pieces into the opposite of reality and figure out what you are trying to say... 
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Posted: 11/28/2007 7:36:47 PM EDT
[#31]
I also smell bad and do not bathe.
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Posted: 11/29/2007 7:11:55 AM EDT
[#32]
Correct, but I think Tommy is trying to say if you had a bullet that was lighter it would have higher velocity and therefore could have about 10-20% more RPMs due to the lighter bullet having the higher velocity. .223 pressure, 75 grain ammo, a 1/9 barrel twist and a short 10.5" barrel will give the lowest velocity with the minimum twist and is very borderline... change any of those... 5.56 pressure, lighter ammo, longer barrel (all give higher veocity and thus RPMs) or faster twist and it is no longer borderline. As a barrel wears it loses velocity over its life... this can become substantial late in the barrels life. What may work with a new barrel in warm weather could end up causing a baffle strike later on and in cold weather. |
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Posted: 11/29/2007 3:01:56 PM EDT
[#33]
Dude- he didn't put that much thought into it but now you'll never know for sure. You should have posed that as a hypothetical question to see how he'd respond. |
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Posted: 11/29/2007 4:13:04 PM EDT
[#34]
Not the exact question but same subject.
If I'm pulling 1 MOAish groups out of a 16" barrel with a 1/9 twist using 77gr Black Hills, I should be ok to use with my pending HALO correct? Is it a safe assumption that getting that sort of groupage at 100 yards that the bullet is stabilizing effectively? |
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Posted: 11/29/2007 5:25:04 PM EDT
[#35]
Like I said in my very first post. Gemtech aka Phil Dater has posted many times that the asymetric baffle design can put side pressure on a heavy boat tail bullet and cause yaw inside the silencer and perhaps a baffle strike. So stable shooter without the silencer is just the first step. The design of the bullet and of the silencer also play a part. I am sure if you contact Gemtech with specifics of your load/rifle combination they will respond with an appropriate opinion.
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Posted: 11/29/2007 5:29:13 PM EDT
[#36]
I would have no problems with the 1:9 without the silencer. My concern was the can. The quote below is why I bought a CMMG 1:7 barrel and I got that barrel today and installed it.
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Posted: 11/29/2007 7:47:47 PM EDT
[#37]
The bullet is stable 100 yards down range. That doesn't mean it's stable within the first 9 inches of leaving the barrel. It may still be getting straightened out. Kinda like taking off from a standstill on your bicycle.
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Posted: 12/1/2007 7:29:13 PM EDT
[#38]
I agree with the post from the first page.
Shoot some paper close and if no keyhole I would probably shoot one through the can. However, I went with the CMMG barrel on my 11.5 build. I have not seen any pics of a baffle strike in the middle of the suppressor unless the can was unthreading or the barrel was threaded wrong. All the ones I have seen have been on the end cap and have been cosmetic. I went with the CMMG barrel because I couldn't get good groups from my 1:9 barrels. I am in no way an expert so I wouldn't believe a word of this. YMMV
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