Molons posts showed IMI Razor 77 grain ammo running well over 2800 fps from a 20" barrel. THAT IS HOT. A full 200 fps faster than what I consider a maximum load.

I really look forward to getting some velocity info on these rounds with different barrels.  I will be sure to check the rounds for pressure signs.

Hooo boy...I just bought 500 rnds (225/G) of this from SGA a month ago.  I shot 30 rnds of it a couple of weeks ago and didn't notice any primer issues or anything else unusual, but I wasn't particularly looking for anything either.  I do recall the brass ejection pattern was different, but don't recall exactly what position it was being thrown.  I'll keep an eye on this thread.

Can you provide general description of firearm?  Barrel and chamber type, etc.

Sure, it's a 5.56 chambered PSA FN made barrel (chrome lined) at 16 inches, 1:7 twist,  with a standard A2 flash hider installed.  Low round count through the gun (less that 800 rnds so far).

Update I got out to range today and shot 80rds.Lot 00225/G with no problems going again tomorrow to see what ammo my Mod 0 likes the best.

Lot 00237/E of the 77 gr, no problems with any of my guns so far.  Mostly shoot it in my 18" .223 Wylde rifle with and without an AAC SR-7 .30 cal suppressor.  It's very accurate, and I bought a lot of this over the last couple of years.

Of the 60 rounds we fired through 3 wylde barrels we had no pressure signs or failures.  This is a small sample but I figured I would share.



The full IMI run down can be found here on www.scienceofthegun.com

My AR that has no problem with the IMI 77gr 'Razor-Core' is full 16" C/L, 5.56, 1:7, modified HBAR, mid-gas, by CMMG. The IMI turned out to be the best accuracy of six loads I tried the last time I went out with it. I think the guns that have problems with it could have problems with the chamber or headspace which cause the hotter round to 'stick' in the chamber a split-second longer because of it's greater rate of expansion, allowing room between the case head and bolt face for the primer to blow out. Shoot the ammo your gun likes.

I've shot about 100 rounds through my Noveske 18" SPR w/ Intermediate gas and have had no issues.

This problem should not happen in numerous Colt and LMT M4s- all with low round counts.  Previous lots of IMI 77 gr razor core did not have these problems in same guns.  It is definitely an issue with ammo/ certain lots

AR15: BCM
Model: BCM4
16" chromed line 1/7 twist barrel.

I  bought this ammo from SGAmmo months ago and went to the gun range today. I fired  60 rounds of IMI 77gr razor core ammo lot number: 00229/F and I did not have any issues firing this ammo. I also fired 30 rounds of IMI 69gr razor core lot number: 00228/F and had no failures either. I bought the 69gr from Cabela's sometime ago too.

Agreed. My experience as well after shooting 3 or 4 different lots in the same guns, prior to seeing pressure spikes and popped primers in Lot 225/G.

Lot 00237/E and had no issues. 20" velocity 27xx something in 50°F weather:





 

What online source has the best prices for th IMI 77gr Razor Core?

First "malfunction" I have had with my AR was due to the IMI Independence M193 blowing a primer and the primer landing on a locking lug on the bolt. Luckily my genius buddy that was shooting it at the time started ramming the FA immediately

+1.  Per "The AR-15, Volume 4", pg. 105, peak chamber pressure of 556 ammunition in 223 chambers can be measured as high as 75k PSI and I would think could cause the problems noted in this post. Of course hot ammunition- either "loaded hot" or with a high internal temperature may cause the same thing.  In  my experience and anecdotal evidence, many barrels marked as 556 actually measure to be a solid 223 chamber.
My barrels (measured using Ned Christiansen's .223/5.56? Gage):
- BCM 16" BFH, chrome lined, 556, 1:7= measures a tight 556.  Fires IMI (my chosen primary supplier) including 00225/G fine and is the only barrel I have fired this in.
- Bushmaster 16" pencil circa 2003, 556, 1:9= measures 223
- PSA 10.5", 556, 1:7= measures 223
- Green Mountain 10.5", chrome lined, 556, 1:7= measures 223  ( I will fire the IMI 77 OTM in this barrel in the near future)
My guess is the less expensive barrel manufacturers change the reamers less often than required to maintain 556 chambers with the 556's longer freebore/throat, which is also where my 556 barrels that measure as 223, touch the gage.

I will chronograph loads in the BCM BFH and Green Mountain barrels this spring after it warms up and I have completed the new rifle range I am building.

SG Ammo

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I had issues with CBC 77gr OTM in my SR15. Exact same symptoms.

(I fully realize we're talking about different rounds.)

My BCM runs it fine.

My KAC and my PSA (complete spectrum, cost wise) have the same problems as the OP.

I'm starting to wonder if this load (in general) is problematic to some AR systems. Not the first thread I've seen with over pressure signs on an AR15 platform with 77gr OTM loads. Multiple brands of rifles.

My $0.02

BCMs are not the most accurate barrels I own but are not problematic in regards to this ammo. I attribute that to a generous freebore length and dia. However, I fired lot #00229F 77 gr IMI in multiple 5.56 chambers to include BCM, Colt, Bushmaster, FNMI and even a couple Wylde chambers. I tried lot # CBC 036/16 77 gr in a Colt SOCOM barrel, a Krieger/Wylde chamber and a 20" govt profile FNMI barrel. So far (fingers crossed!) I have had no problems but have not tried either one in a verified .223 chamber and don't plan on trying.

Per my earlier post with 223/556 chamber measuring, the BCM was the only chamber that measured 556 with the less expensive barrels measuring as 223.  I reamed all to 556+ specs.  Even though the chambers measured a solid 223, very little metal was removed from each chamber to bring them to 556 specs and that was in the leade area.  

Yesterday I shot a new- previously unfired, chamber reamed, Green Mountain 10.5", 556, 1:7, chrome lined barrel with various ammunition types (150 - 200 rounds), including one of my favorites of IMI 77 gr OTM lot 225/G (only 10 rounds for zero checking) with no issues.  Since I have never had any ammunition problems I am not able to make an apples-apples comparison with a chamber failing, then reaming, then passing shooting tests, to verify tight chambers may be exacerbating any issues.
If interested- The 223/556? gage and 556 reamer are listed on this page: http://m-guns.com/tools.php.  High quality products that can ensure chamber sizes are correct.

does reaming a chamber after the chroming process remove some of that chrome plating?

I look at it like this- the reamer is just touching up areas that were not machined exactly correctly in the beginning.  And for the most part, is not reaming an entire chamber.  Excerpt of the instructions with the reamer:  ..."There is no issue with removing the chrome from the areas reamed.  I have sectioned several chromed barrels in this area and found that the chrome does not always last in this area anyway.  Besides- safety and reliability trump all else."  

Also in the instructions, "My experiments have actually shows an overall improvement in accuracy after reaming."  And this makes sense to me as slowing 556 pressure ammunition to 223 levels generally improves accuracy.  I would think this more so in some chambers with a shorter leade causing pressures in the 75k PSI range.

When I reamed three of my barrels- one chrome lined, there was some metal on the reamer but nothing that was obviously chrome plating, to my eyes anyway.  And the overall reaming process was far less than I expected by the gaging I had performed earlier.  So at least in my cases, there must have been just enough "extra" material in the leade area to cause the gage not to drop down fully, yet not enough to cause much reaming except on the Bushmaster barrel, which took off more material that the others. Actually, most of the material on the reamer was removed from the Bushmaster barrel, which I do not believe is chrome lined.

Recently purchased several boxes of IMI 77gr lot #00228/f and several boxes of IMI 55gr M193 lot #00245/f. Shot all with zero problems, no pressure signs or anything. Recovered all brass, processed and reloaded with 69gr Sierra HPBT w/ 21.5gr LT-32. All shot with no problems. I like the IMI brass and I think it is as good as LC YMMV.

Gun info
Anderson lower
YHM upper
Green Mountain 20" barrel
Fail Zero BCG
Nikon 4-12X40 BDC scope

Vince

Fully agree.  Ned's 5.56 reamer is a must have if you wish to run hotter ammo in a variety of aftermarket barrels.  I've seen it turn bushmaster barrels from blowing primers every mag to running perfectly.  

Whatever chrome is removed, would have been lost anyway in the first k rounds of hot ammo.  

Michiguns.com has gotten a good bit of money from me over the years...worth it.

I shot 90 rounds of lot# 00225/G today through two Colt LE6920s.  No signs of pressure.