Posted: 7/22/2010 2:52:15 PM EDT
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I was at our range today and spoke with one of our PD armorers. Here is the back story first. Our PD purchased some 5.56 training ammunition. In approximately 2000 rounds fired, we had 24 primers blow back out of the bullet cases resulting in a lot of downtime because of the primers lodging in different areas of the receivers, trigger groups, etc.and not to mention some interesting times on the firing line.
The rifles are Bushmaster M4A3 sleect fire with 11.5 inch barrels and Surefire supressors. These are our SWAT rifles (28 total). Our first thought was the ammunition. I don't remember the brand (I think Federal) but it is standard 5.56 62 grain ball ammuntion. After haggling/arguing with the ammunition manufacturer and having the same problem with a smaller second shipment we looked to the rifles. The rifles ARE STAMPED 5.56 on the receiver, however, when the chambers were checked with a guage they were 223 chambers on all of the rifles. This was confirmed by Bushmaster who has asked for our PD to begin sending the rifles beck for reconfiguration. According to Bushmaster this is the problem that is causing the blown primers. THIS IS NOT A BUSHMASTER RIFLE BASH THREAD but a heads up if any other PD is having a similar problem. I guess this settles the 223 and 5.56 chambers are the same argument. |
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I didn't think Bushmaster made .223 barrels, except for their heavy bull match barrels. Were the barrels marked as Bushmaster ones? Were these rifles purchased directly through Bushmaster? Bushmaster THINKS they make 5.56mm chambered guns. But I've got a few brls from them that were closer to .223 than 5.56mm. Someone is probably using their tools too long. |
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Fire some of that ammo out of known good guns. I suspect the ammo is the culprit based on your account of the problem. That is exactly what we thought, that it was the ammo. But after we guaged the chambers and called Bushmaster they agreed on the chamber issue and are repairing the rifles. |
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Once you get a Ned Christiansen reamer and start reaming many different types of barrels.....you'll be surprised at how many are not true 5.56 chambers as marked. I've had Colts and LMT's that reamed out a bit as well as Bushmasters,DPMS and LWRC.
I even had a Knights SR15 that was blowing primers. We ran Ned's reamer into the chamber and problem disappeared. Its good to know that Bushmaster stepped up to make things right. |
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I'll put this as politely as I can. I hate our fucking select-fire Bushmasters. The F/A ones are marginal. The burst guns can eat shit. +1 
shouldnt be like this- for the $ spent, we shouldn have these issues on equipment they knowingly sell us with the purpose of betting our lives on. |
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While going at it with a reamer would definitely fit the tolerances issue, would it not remove the "chrome lined" feature?Eating through the chrome and leaving bare steel in a place that may or may not even be cleaned sounds like an invitation for rust and future feed/extraction issues. |
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I see that you said it is stamped 5.56 on the receiver. Is there anything marked on the barrels themselves? The receiver markings can be anything, a lot of manufacturers are going to Multi markings. Normally the barrels will tell the true story of what you have. |
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I see that you said it is stamped 5.56 on the receiver. Is there anything marked on the barrels themselves? The receiver markings can be anything, a lot of manufacturers are going to Multi markings. Normally the barrels will tell the true story of what you have. I'm pretty sure Bushmasters says all their barrels are 5.56 except for match barrels that are .223. |
| TxLawDog, some of the SWAT guys at my dept. had the same type of issues using Colt factory Commando rifles with Surefire supressors. The ammo was Federal manufactured but I'm unsure which type ball or 55 Gr Nosler. The primers were found mostly under the trigger and caused the guns to not select into the safe position. The first gun they found this in...Officer couldn't get it into safe so he rocked selector to auto and back toward safe. This caused a three+ round string of fire, no finger on trigger. This was duplicated on another gun while they were at the range using the same ammo. Both times they found the primers under the trigger. Hope this helps. |
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I think it is more suppressor related.
Usually when the bullet passes the gas tube port in the barrel, the bullet is out of the barrel, and pressure in the barrel is decreasing as the bolt begins the extraction cycle. Because you are using suppressors, the bullet hasn't cleared the suppressor, and the pressure in the barrel is still pretty high, as the bolt begins the extraction cycle. When the back of the spent casing is no longer flat against the bolt face, the residual pressure is popping the primer out. You might want to try an adjustable gas tube or "pigtail" type gas tube to delay the beginning of the extraction cycle a few milliseconds. Or try a heavier buffer. |
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Heavier buffers may delay bolt unlocking, but they'll also reduce cyclic rate. Not a big issue if you're expecting that. In my opinion these firearms should be using ammunition with crimped primers, in addition to having correct chambers, just for added reliability. |
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I've not had issues firing suppressed weapons, but I've had a lot of primers pop loose with some bad frange. I'm assuming you've fired them with and without the cans? Yes. The rifles are run both with and without the suppressors but I don't know to what percentage. I am on our PD Firearms Advisory Committee and there is a meeting on several issues this week and I will ask about the suppressors specifically. |
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Quoted: Quoted: I've not had issues firing suppressed weapons, but I've had a lot of primers pop loose with some bad frange. I'm assuming you've fired them with and without the cans? Yes. The rifles are run both with and without the suppressors but I don't know to what percentage. I am on our PD Firearms Advisory Committee and there is a meeting on several issues this week and I will ask about the suppressors specifically. Have you talked to Surefire? I think their rep lives in Round Rock. |
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I would have called Ned Crhristiansen and got his throat reamer to fix them myself. Faster and probably cheaper in the long run. This is the answer. I have seen a number of Police Bushmasters that would blow primers due to their use of an undersized chamber and oversized gas port. Bushmaster's target market is not LE or MIl. They build to a civi standard where .223 ammo is more common and buyers complain if the rifle won't function with crappy wolf underpowered ammo...so you get smaller chambers and larger gas ports. For the guns you already have...trade them in on Colts. Seriously...it will cost less in the long run and you won't have to monkey with the guns constantly for years to come. If you can't do that, get the reamer above and use it. It is the best solution if you have to keep these guns. |
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I was at our range today and spoke with one of our PD armorers. Here is the back story first. Our PD purchased some 5.56 training ammunition. In approximately 2000 rounds fired, we had 24 primers blow back out of the bullet cases resulting in a lot of downtime because of the primers lodging in different areas of the receivers, trigger groups, etc.and not to mention some interesting times on the firing line. The rifles are Bushmaster M4A3 sleect fire with 11.5 inch barrels and Surefire supressors. These are our SWAT rifles (28 total). Our first thought was the ammunition. I don't remember the brand (I think Federal) but it is standard 5.56 62 grain ball ammuntion. After haggling/arguing with the ammunition manufacturer and having the same problem with a smaller second shipment we looked to the rifles. The rifles ARE STAMPED 5.56 on the receiver, however, when the chambers were checked with a guage they were 223 chambers on all of the rifles. This was confirmed by Bushmaster who has asked for our PD to begin sending the rifles beck for reconfiguration. According to Bushmaster this is the problem that is causing the blown primers. THIS IS NOT A BUSHMASTER RIFLE BASH THREAD but a heads up if any other PD is having a similar problem. I guess this settles the 223 and 5.56 chambers are the same argument. Hmmm...........we have the same set up, no problems so far but I'll have our armorer check them out........thanks for heads up. |
COLT