450Bushmaster.net

First off, I want to give a big hello! I lurked here for a bit and looted the information y’all have shared when I built my AR pistol and I’m happy to say its completed! Before I get asked why a pistol, I built it to hunt deer with in Illinois. Yes, its legal to hunt with as long as the magazine is not inserted (I asked the IL DNR to confirm before I even built the gun and they said I was good to go). I’m very happy about my lil’ thumper and I have already taken it on a few hunts this weekend.

Now for my problem. I wasn’t sure if this was the correct location for this question as it is more ammo based, so please pardon me if I posted it in the wrong area. While sighting my gun in, I experienced a hang fire. I was doing the initial function test/sighting in and I pulled the trigger, I heard the hammer hit, and then the expected boom. I am using Hornady 250gr factory ammo and a gun that I built. At the time of that hang fire I didn’t think much about it and didn’t experience any more that day. Fast forward to yesterday and I am out hunting. I have a deer come in, I take my aim, pull the trigger, and once again I hear the hammer hit and then a boom. Luckily enough I missed the deer completely, but this misfire “trend” now has me concerned.

I have the problem narrowed down to a few areas that I think could cause it. First is the ammo, which is an obvious choice. I have emailed Hornady and I am waiting on their response. I really hope it’s the ammo, but I want to see if anyone else has had this problem. I reload but haven’t had time to develop a load for the 450 yet.

The second area that may be a problem is the trigger. I “modified” the trigger to have a cleaner break. This trigger is a crappy DPMS trigger that I wanted to mess around with. I heat treated and quenched the entire trigger and polished the sear to mirror finish. I was mainly concerned with the sear faces and paid no attention to the hammer, so I could have softened the hammer to the point where it is deforming when it strikes the firing pin, but I don’t know if that’s plausible or logical. I did shoot this lower, using a different upper, before the gun was complete just to ensure it all worked which it did.

The final problem area is the lube I used. I generally run my ARs on the dry side. I don’t run and gun or throw thousands of rounds down range a month and I’m lucky to shoot 500 rounds a year so a massive amount of lube is not needed when I shoot. I spray and wipe off the internals with RemOil, but for some reason this time I didn’t. At the range I got a free tube of lube. Being a sucker for free stuff I took it and properly lubed my bolt, firing pin, and BCG up. What I really think happened is the lube “gummed up” in the lower temperatures and slowed down the firing pin which caused a light strike on the primer. Either way my BCG and bolt are getting degreased tonight and lubed my normal way.

If you have any experience with this or have any insight please let me know! Also sorry for the long post.

I like pistol builds, have a 12.5" 450B myself, with a 10.5" (for a subs only build) being made.

What barrel, buffer weight, and spring are you running?

I have to say, I don't remember anyone having hang fires with factory ammo. It sounds like it could be a crimp issue or the factory ammo is undercharged.

I recommend tearing down the BCG, removing all the current lube, and hose it down with the Rem Oil. I'm not a fan of the Rem Oil for the long haul, but for break-in it's perfectly fine. It's really not a bad a lube for cold weather, because it has Teflon in it, and doesn't seem to gum up very fast. Long term corrosion protection isn't so great, though. For new builds you want to run them EXTREMELY WET. it keeps things slick, and helps pull the metal and finish that wears off, away from contact area's. Now because you are currently hunting with this rig, I recommend also manually cycling the action a couple hundred times (with no mag or ammunition in it, of course), dismantle, clean off the oil, then re-oil, but don't go crazy if your taking it back out hunting. That should smooth things out a bit for you, for now.

I would also check and make sure that hammer is still in spec. If you can, I would recommend replacing it. You messed with the heat treat (or surface hardening, whichever was used on it), and could end up with issues down the road.

It could be lubricant stiffening. I grew up in MD. My Dad still lives there. He brought his Belgium Browning .30-06 BAR out with him to hunt deer in norther MN. He experienced a failure to fire one cold morning using factory ammo. Back at the hotel room I, having brought everything but the kitchen sink up north with me, tore the rifle which I had shot in 60 degree weather, down. I flushed the lubricant he had used out, stinking up the room in the process and applied some mil spec CLP. It was just as cold the next three mornings and he bagged two deer with the same rife and same ammo.

Easy test. Remove your BCG and put it in the freezer for an hour or so with the bolt in the forward position. Remove it, grab the back of the firing in and slide it back and forth. If its sluggish, de-grease it and the raceway and find a new lubricant. If you used the same lubricant on the FCG, then do the same for it.

Hoot

Bmt85-

Barrel is from Ritch’s Precision, 10.5 in, black shot peened finish. The buffer is a AR Stoner H2 Heavy and the buffer spring is a JP tuned and polished spring.
One thing I omitted, unintentionally, is that I did not buy a bolt with the barrel. The bolt came on an AR stoner BCG and hasn’t been head spaced to my barrel. I have read a lot about head spacing and if it is needed and I decided that I wasn’t going to YET. I feel that it is ultimately a must when you mash up parts like I did but being impatient and not having a gunsmith around with the go/no gages helped me make that decision.

I honestly don’t think I have degraded the hardness of the hammer. When I preformed the heat treat I was in a materials class doing the same type of hardening on different metals. Not exactly the same at home than in a lab, but for what I wanted to do it worked. I do plan on replacing the trigger eventually and it may be sooner rather than later. I have a RRA 2 stage from a different gun I can toss in it for the time as well.

I will cycle the action thoroughly this evening. I never thought about doing that so thank you for that suggestion!

Hoot-
The only reason I even thought it was the lube is that we NEVER use heavy lubes in our duck guns after a bunch of them froze up after using other things(WD40). Why I didn’t think about that when I lubed my pistol, I have no idea. I will try your suggestion tonight.

Im still waiting on hearing from Hornady.

I’ve used the same original Bushmaster 450b bolt in 4 different barrels over the years. Never worried about headspace, though I should have. Worked fine. Would never think of doing that on a non-MSR rifle.

Hoot

I’d try the Rock River trigger. My 450 has the 2 stage NM, and it’s been great. It’s been in several different guns, and has been 100% reliable. CLP is my lubricant of choice. Never had problems with it in cold weather.

I always wipe the firing pin completely and trust what remains on it to lube the channel it runs in. You can get a hydraulic lock on the firing pin, if it is over lubed. That happened to me on an AR type BCG on my UTS-15 shotgun. In that case, the gun would not fire until I wiped the firing pin off.

If you are getting a weak hydraulic lock, it could be slowing the firing pin down enough to introduce a delay between pulling the trigger, the hammer hitting the back of the pin, and the pin either sticking momentarily or moving slowly to strike and detonate the primer.

if you want to test if its an ammo - find another gun to shoot it in.