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"Hybrid" SAAMI spec chamber

SnkBit

Sergeant
Full Member
Minuteman
Dec 10, 2009
212
30
Amarillo, TX.
What the hell is a hybrid SAAMI spec chamber? I bought another AR this week, a Bushmaster Predator. The Specs say that it is a 556/.223 chamber and state that it has a hyrid spec chamber. I fired what I had left of some cheap 556 ammo and had countless FTF and a few FTE's. I had to pull one manually with the charging handle and thats when I noticed how difficult the extraction was. I'm sure that it was over pressure. The Hornady TAP I fired through it functioned flawlessly. Did I get some piece of shit barrel?
 
Re: "Hybrid" SAAMI spec chamber

I don't know what hybrid chaimber is,but I asume it just another word for Wylde chaimber which is built to shoot both 5.56 and 223, not as long of a throat as a 5.56, but it has a longer throat than a 223 .

 
Re: "Hybrid" SAAMI spec chamber

Check the gas key and see if it's loose . Did you run the TAP before or after the 5.56?
what does the case heads look like any pressure sighn?
 
Re: "Hybrid" SAAMI spec chamber

Ran the TAP after the cheap crap. Case heads are typical of an AR, a little beat up but haven't "flowed". I will check the gas key just to be sure.
 
Re: "Hybrid" SAAMI spec chamber

FTF Could be mag related or short stroking from low gas . FTE Could be from not enough gas pressure or not enough oil.
The FTE, was this still closed bolt or did the Bolt close on an empty dude ways, bad ejector spring can cause this.
hard to tell without seeing it in person .and diffrent loads stress diffrent components .
 
Re: "Hybrid" SAAMI spec chamber

I tried multiple mags of known quality, same thing. The FTE was still chambered. It had opened the bolt and stuck about 1/4 of the way back. It was somewhat difficult to pull, thats why I figured excessive pressure. You think it might have been low pressure and wasn't producing enough gas to fully cycle the bolt? I was thinking it was excessive drag from the swollen case causing the bolt to short stroke.
 
Re: "Hybrid" SAAMI spec chamber

I have seen case heads and rims tear off from over pressure .
But if its sticking in the chaimber that's not good and it may have chaimber issue.Try cleaning it and brush out the chaimber .
Is this a factory rifle?

What is the barrel lenght and what gas length?
 
Re: "Hybrid" SAAMI spec chamber

It's a factory Bushmaster Predator, 20" barrel. These are the only two types of ammo that I have put through it so far. Seeing as the TAP worked flawlessly I assume it's an ammo problem. The thing that concerns me is that the cheaper ammo didn't present any problems in any of my other rifles.
 
Re: "Hybrid" SAAMI spec chamber

My partner had a Barrel that would not run 5.56 even though it was stamped so. He could only run 223 he sent it back and they polished the chaimber and it still only ran triable with 223 .

I will ask him the brand when he comes on duty tonight.
 
Re: "Hybrid" SAAMI spec chamber

Here we go again. The BM Predator has a tight match chamber that is known to cause FTE, double-feeds, etc. It most certainly does not have a Wylde Chamber...would work great if it did. If you want to keep this wonderful upper, then you will need to experiment to see which factory ammo it can feed well. You might also improve things by polishing the chamber. This is a well-known problem: check around on the forums. Tight chambers and ARs don't belong together. On a positive note, they seem to be pretty accurate uppers. I ditched mine after I returned it to BM and they said "everything is fine."
 
Re: "Hybrid" SAAMI spec chamber

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scooter-PIE</div><div class="ubbcode-body">Here we go again. The BM Predator has a tight match chamber that is known to cause FTE, double-feeds, etc. It most certainly does not have a Wylde Chamber...would work great if it did. If you want to keep this wonderful upper, then you will need to experiment to see which factory ammo it can feed well. You might also improve things by polishing the chamber. This is a well-known problem: check around on the forums. Tight chambers and ARs don't belong together. On a positive note, they seem to be pretty accurate uppers. I ditched mine after I returned it to BM and they said "everything is fine." </div></div>

Thanks for the info. I don't really browse any other sites than the Hide so I'm not likely to find any info if it's not here. From here on I will be handloading for this rifle. I'm guessing I will need to use the small base dies. Surely this thing will feed reliably with small based handloads......right?
 
Re: "Hybrid" SAAMI spec chamber

If you are going to be handloading, then it probably won't be a concern.
One way to find out what is going on is to SAFELY AS POSSIBLE, chamber a live round that is difficult to extract, with just your finger.
Does it want to stick in the chamber?
If it doesn't than the base was sized appropriately and the difficult extraction was likely due to the shoulder needing to be bumped.
Chamber the round with the bolt/carrier and see if extraction becomes difficult. (Beware of the real possibility of a slam fire)
If it's not than the shoulder is fine.
If the shoulder, and base are fine than it is likely a rough chamber.
You may be able to polish it.
Look in there with a flashlight and see how rough it is.

Also, new bolts and chambers are usually tight for the first 25-50 rounds as they mate.

You may have some fat ammo that isn't happy in a tight chamber.
Heed the above advice when setting your re-sizing die.
SB dies are almost never necessary.
 
Re: "Hybrid" SAAMI spec chamber

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ASM1</div><div class="ubbcode-body">I have seen case heads and rims tear off from over pressure .
But if its sticking in the chaimber that's not good and it may have chaimber issue.Try cleaning it and brush out the chaimber .
Is this a factory rifle?

What is the barrel lenght and what gas length?</div></div> also few i had seen as well is badly made barrels and bad ammo too
 
Re: "Hybrid" SAAMI spec chamber

You can also ream it out to a Wylde or 5.56 chamber and then shoot 5.56 or .223 ammo. I have a 5.56 reamer if you'd like to borrow it. It is easy to use.
 
Re: "Hybrid" SAAMI spec chamber

That weapon is made to hunt with using match grade ammo and capable of sub m.o.a. with heavy bullets (1/8 twist) if fed properly.If you want to run crappy ammo either "polish" the chamber and hurt your accuracy or run the good stuff.You want to spray and pray buy a AK. If you want accuracy run a match chamber fast twist AR. As you said TAP runs fine. If you want to save money reload to TAP specs.Leave the cheap crap for "zombie hunters"
Scot
 
Re: "Hybrid" SAAMI spec chamber

I am definitely not interested in modifying the chamber for the purpose of being able to shoot cheap ammo. I only shot that ammo through it in the first place because I had about 60 rounds that needed to be used up and had not shot the new gun. I'm going to hand load for it with both the 75gr Hornady and some Berger VLD's. If it feeds and functions fine with those loads then I won't mess with it. Is the use of small base dies really necessary? Should I try a few rounds with standard base dies and see how they feed and eject before I start overworking my brass with the small base dies?
 
Re: "Hybrid" SAAMI spec chamber

The regular dies will most surely be just fine.
Take your time setting your sizing die.
Hand check re-sized brass, and adjust your dies accordingly.
Sometimes re-sizing dies contact the shell-holder, and they still don't bump the shoulder far enough.
 
Re: "Hybrid" SAAMI spec chamber

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scot</div><div class="ubbcode-body">That weapon is made to hunt with using match grade ammo and capable of sub m.o.a. with heavy bullets (1/8 twist) if fed properly.If you want to run crappy ammo either "polish" the chamber and hurt your accuracy or run the good stuff.You want to spray and pray buy a AK. If you want accuracy run a match chamber fast twist AR. As you said TAP runs fine. If you want to save money reload to TAP specs.Leave the cheap crap for "zombie hunters"
Scot </div></div>
I have run all sorts of ammo threw mine: Federal, Black Hills, etc. Most of them had feeding issues. I've never heard of anyone saying you will hurt accuracy by polishing the chamber. In fact, its the competition shooters who recommend this practice. I think an AR should feed any type of ammo flawlessly: that's my standard. Since switching to a Wylde chamber in my ARs, have not had a single problem.
 
Re: "Hybrid" SAAMI spec chamber

If you check my post you will see "polish" Because it is commom for chambers to be over "polished" trying to make them feed .My point is the Predator 1/8 likes heavy 75/77 gr match ammo and shoots it rather well.Do to the mad rush after the fall of the whitehouse and the ecomony taking a dump. You can pick up "beater" uppers for next to nothing used at the pawn shop.That have 1/9 loose chamber barrels and shoot steel case crap all day long. It's just two push pins away. Why "fix" something that ain't broke for the price of 500 steel case rounds switch to the "beater " and Rambo away then hunt with the accurate rig.
Scot
 
Re: "Hybrid" SAAMI spec chamber

Ok, I shot 40 rounds through it today. They were reloads sized with a RCBS standard full length sizer die, 23gr RL-15 and Hornady 75gr BTHP's. I was getting flattened primers from that loading and it FTF about 3 times. It would eject the spent round but not cycle far enough to scrape the next round from the mag. I also shot 5 handloads at 23.5gr of RL-15. It flattened the primers as well and began to flow into the ejection port. It failed to feed 3 of those 5 shots. I checked the buffer tube and spring for any possible problems. I also checked the gas key, its tight and staked. Im going to check the gas tube for possible cracks or other leakage. I would figure with loads that were showing pressure signs it would be working the bolt extra hard, the the opposite. I'm also going to try to run the bolt a little more wet for a while to try and "marry" the bolt and receiver. Anything else you guys see that I might take a look at?
 
Re: "Hybrid" SAAMI spec chamber

I would wager that you're using Winchester small rifle primers.
They flatten at low pressures.
They pierce easily as well.
They produce terrible rifle primers IMO.

24.0 of RL15 is a pretty standard "safe" load with a durable primer, under normal conditions.

No more rounds sticking in the chamber?

Did you do what I suggested in my earlier post?
That really may help you to figure out what is the problem.
You see, if a round wants to stick with just finger pressure, you may be jamming into the lands causing elevated pressure.
A pic of a recent case head would help too.
There are other problems that it could be as well.
You will just have to rule out one thing after another.

I would also pay close attention to the gas block and tube.
The gas block could be slightly misaligned with the barrel port, there could be a burr there somewhere, the gas block may have a leakage path.

You may want to disassemble the gas block to check it's alignment.
 
Re: "Hybrid" SAAMI spec chamber

Yeah, I tried what you said, all is fine. I did notice that compared to my other AR's the fit between the gas tube and the gas key on the BCG seems loose. It looks like there is a lot of carbon build up in the upper receiver where the junction is, more than any of my other AR's. I'm leaning toward a gas leak at this point. Oh, and no there were no failure to ejects.
 
Re: "Hybrid" SAAMI spec chamber

Well I guess you could dial caliper the tube and the inside diameter of the carrier key.
Find out where the slop resides, and replace that part.
If the key should need to be removed, dremel off the staked area and an allen wrench should be all that's required.
 
Re: "Hybrid" SAAMI spec chamber

Ok, checked the gas system and all seems in order. I lubed the bolt up like an old whore, loaded some more ammo and headed back to the range. The rifle shot quite well at 23-23.2gr of rl-15 behind the 75gr Hornady. As I increased the charge the rifle suffered it's first FTF at 23.6, 23.8 yielded 50% FTF's and 24 was near 100% FTF. At 23.8 and 24 it also failed to lock the bolt open after the last round was fired. At first the opinion from a fellow shooter at the range was that the bolt was over worked and was coming forward before the mag could catch up. After watching, he said that it appeared to be short cycling. Why would this rifle short cycle with hotter loads? FYI, I intend to load for this rifle around the 23.2 mark where it had no malfunctions today and was also the most accurate. It annoys me however that this rifle is so finicky.
 
Re: "Hybrid" SAAMI spec chamber

So the rifle "fails to fire" (FTF) when the charge weight is upped?
From your description it sounds like it's a failure to extract, or maybe eject or something like that.