Bolt is not returning to battery

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: Bolt is not returning to battery

Postby mcurbo » Tue Mar 20, 2018 6:29 pm

It is a 20 inch barrel. I have been working the charge handle quite a bit and it is better. Thanks for the heads up about the gas block. Unfortunately I can't do much about the twist rate. I am shooting 250 grain Hornady, and to be honest I will have to research what my options are for a lighter bullet. Again, I am new to this, but when you refer to a gas event waiting to happen with my set up, what are you referring to and can I do something to correct it? Thanks again for the feedback.
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Re: Bolt is not returning to battery

Postby Bmt85 » Wed Mar 21, 2018 1:42 pm

Is it actually a rifle length gas system? Take a measurement from the front of the upper receiver to the back of the gas block. It doesn't have to be exact, just ballpark it off a tape measure, scale, ruler, whatever. What do you get? If it is a rifle length gas system, that's probably your issue. I have a 20" Blackhole Weaponry barrel with a rifle length gas system, and it won't cycle 100% of the time with factory ammo. It will most of the time, but not 100%. I expected that when I ordered the barrel, plus I handload, so it's not really a concern to me. You might be able to open the gas port a touch, depending on what it is.
Last edited by Bmt85 on Wed Mar 21, 2018 1:49 pm, edited 1 time in total.
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Re: Bolt is not returning to battery

Postby Bmt85 » Wed Mar 21, 2018 1:47 pm

As to what Sheepdawg is refering to, the standard twist rate for the 450B is 1:24, so a 1:14 is almost double. When you increase twist rate, the pressure usually goes up for a given load. I didn't see any mention of a special rifling being used, so I'm assuming it is a standard 6 groove Enfield rifling, which you will most likely see a pressure increase. With too much of an increase, you can get a bad pressure spike, and bad things can happen. With the 450B factory ammo, you should be ok, but I would really like to see what your primers look like, what your case head growth is, and what the length change is. Handloading will be able to work around the twist rate, to a point, but chances are it's going to require a slower powder than normal, especially for the heavies. If trying to find factory ammo, you might be severely limited because there isn't a whole lot of options.
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Re: Bolt is not returning to battery

Postby mcurbo » Wed Mar 21, 2018 7:35 pm

My approx measurement from the front of the upper receiver to the gas block is 13-14". I am only using the Hornady Black FTX right now, but I am starting to piece everything together to reload. I just picked up another 100 rounds of the Hornady and while I have been interested in reloading for a while, the 450 BM has gave me a reason to start, so hopefully as I start learning about the ins and outs of that I can tweak my loads to make up for the twist rate (will probably be asking a lot of questions in the near future...). As far as cycling, I could be wrong, but it seems that the few times I have had an issue, it seems that it is not grabbing the rim and extracting properly. I believe one time it just didn't catch it at all, and the other it looks like it grabbed it thin and literally flipped the casing straight up causing a stovepipe. I just changed to the black follower, even though I felt decent about the feeding, and I won't know until tomorrow when I shoot it, but I may have made it worse since the rounds seem to be much higher in the magazine now and I do not like the nose attitude, plus now the bolt catch when empty is not working.

Bmt85, I have been collecting the spent brass since I am definitely going to try handloading. Tell me what measurements you want me to get, and I would appreciate your help in at least pointing me in the right direction for what I am going to use for reloads. Like I said, I am new, so there is a lot of learning, and I appreciate everyone's input and patience...

Mike
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Re: Bolt is not returning to battery

Postby Hoot » Wed Mar 21, 2018 9:01 pm

The biggest factor with your twist rate and reloading is that you should take the recipes developed over the years using a 1:24 barrel and pretty much forget them. That's not a bad thing as it will force you to learn more as you develop loads that work for your rig. IMHO, the most serious issues that could arise as twist rates speed up is when you are approaching maximum loads for a given combination of powder and bullet. We already know that a 1:10 twist barrel is out there and the earth's poles haven't reversed. The lighter bullets can go through as much as 3 accuracy nodes as you work up from lightest practical to max charge in a 1:24. Its not a huge loss if you can only work through 2 accuracy nodes with your faster twist before reaching maximum charge for a given bullet. At least there will be accuracy nodes to strive for. Yeah, it'll mean more R&D which equates to more money spent but I personally enjoy experimenting myself. When I happened upon this caliber, I was not a fan of black rifles. My efforts before that were with other style rifles. There weren't may published loads at that time that weren't liability lawyer approved but I had a feeling the "soil was fertile". Working on developing loads that my rifle liked was a good on ramp to appreciating the AR platform. We're programmed internally to always be trying to find a "better mousetrap". That's who we are. Nothing makes me more uncomfortable that some new guy checking in, who wants to know how hot they can load this caliber, right out of the chute. That's not the right mindset for getting into reloading. Nor is how cheap you can produce a load, regardless of its performance. Somewhere in between those two goals lies the lion's share of the members here. (thankfully) I don't know anyone else with a 1:14 twist barrel so your work will leave behind a legacy for future 1:14 owners. I can't say I'm thrilled about the rifle length gas system it appears that you have. IMHO, that adds more of a challenge for finding a lot of bullets that will be happy in your bore than the twist rate. I know because I have a 450b upper, sitting on the shelf in the shop, with a 1:24, 20" barrel with a rifle length gas system. As fussy as the day is long with what bullets it likes below 300gr. I could install a low profile gas block over that port and re-drill a mid length one and I have the means to pull that off well, but instead, it just sits on the shelf, a reminder of the risk you take listening to someone who seemed to have a good idea for a better mousetrap. Image

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Re: Bolt is not returning to battery

Postby Texas Sheepdawg » Thu Mar 22, 2018 12:15 pm

All I am going say is that 1:14 twist scares the crap out of me. I just can’t get my head around it.
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Re: Bolt is not returning to battery

Postby Hoot » Thu Mar 22, 2018 1:23 pm

Texas Sheepdawg wrote:All I am going say is that 1:14 twist scares the crap out of me. I just can’t get my head around it.


Nor the two members with Ruger #1's in 450b with their 1:10 twists. :shock: I'm waiting for pitted bore to jump in here any time now.

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Re: Bolt is not returning to battery

Postby Texas Sheepdawg » Thu Mar 22, 2018 1:49 pm

Definitely don’t want to send thin jackets down those......OMG. So then you gotta think about that twist and a thick copper jacket or solid copper bullet. Pressure city.
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Re: Bolt is not returning to battery

Postby Bmt85 » Thu Mar 22, 2018 2:13 pm

mcurbo wrote:My approx measurement from the front of the upper receiver to the gas block is 13-14". I am only using the Hornady Black FTX right now, but I am starting to piece everything together to reload. I just picked up another 100 rounds of the Hornady and while I have been interested in reloading for a while, the 450 BM has gave me a reason to start, so hopefully as I start learning about the ins and outs of that I can tweak my loads to make up for the twist rate (will probably be asking a lot of questions in the near future...). As far as cycling, I could be wrong, but it seems that the few times I have had an issue, it seems that it is not grabbing the rim and extracting properly. I believe one time it just didn't catch it at all, and the other it looks like it grabbed it thin and literally flipped the casing straight up causing a stovepipe. I just changed to the black follower, even though I felt decent about the feeding, and I won't know until tomorrow when I shoot it, but I may have made it worse since the rounds seem to be much higher in the magazine now and I do not like the nose attitude, plus now the bolt catch when empty is not working.

Bmt85, I have been collecting the spent brass since I am definitely going to try handloading. Tell me what measurements you want me to get, and I would appreciate your help in at least pointing me in the right direction for what I am going to use for reloads. Like I said, I am new, so there is a lot of learning, and I appreciate everyone's input and patience...

Mike


So it appears you do have a rifle length gas system. You might be able to try a lighter buffer or a lighter bolt carrier group to get it running with factory ammo. The cycling issue sounds more like your extractor not letting go of the casings. Pull the bolt, take a case, slip the rim under the extractor, straight it up (compress the ejector), then slowly let off the casing. It should freely move and drop out of the bolt. If it hangs up, that means the extractor is digging into the rim. You can lightly file the corners so they don't hang up of the casing.

As to measurements, do you have calipers and a micrometer, preferably a blade mic?

There are some good guys here who will try to help you. Don't be afraid to ask questions.
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Re: Bolt is not returning to battery

Postby Bmt85 » Thu Mar 22, 2018 2:21 pm

Texas Sheepdawg wrote:All I am going say is that 1:14 twist scares the crap out of me. I just can’t get my head around it.


I don't like it either, but there are more than a few 1:16 twist out there, so it shouldn't be too much worse. Plus, the 458 Socom runs some fast twist rates. The 1:24 works great, but I think a lot of these companies are taking the inexpensive route and getting barrels and/or blanks readily available, but they have twist rates that are more appropriate for different cartridges. Basically they are being cheap and not really caring. This 1:14 though, that's a new one.
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