450 Bushmaster pistol issues.

T/C Encore in 450b anyone?

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450 Bushmaster pistol issues.

Postby androtaker56 » Sun Jun 14, 2020 8:31 pm

Build specs:

Upper: Acme Machining 10.5" 450b bull barrel/toolcraft standard bolt.
Lower: Aero Precision M4E1
LPK: Rock River Arms Standard
Stock: SBA4 With carbine buffer tube
Recoil Spring: CMMG standard carbine
Buffer: Spikes Tactical ST-T2 4oz


My brass is ejecting at 3-4 oclock
First two shots left twist tear marks on casing.
Rest of shots left extractor marking on the the face and side of casings without tearing.

I have access to a heavier buffer spring but would I be better off with a heavier buffer?
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Re: 450 Bushmaster pistol issues.

Postby androtaker56 » Sat Jun 20, 2020 12:21 pm

Got to the range for more testing. This time with a heavier buffer spring. The borrowed spring was actually so heavy that the bolt didnt lock back, I had to load 1 round at a time. Still my rounds were extracting too early. It is strange that my extraction pattern is spot on but my timing is off enough to allow slight rim deforming due to early extraction.

Next test will likely be a h3 or h4 buffer.

Lesson learned, even the heaviest spring will not slow early timing issues.
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Re: 450 Bushmaster pistol issues.

Postby androtaker56 » Sat Jun 20, 2020 5:17 pm

Moved buffer weight up to a st-t3 or H3 buffer, and holy cow did it amplify the recoil. It feels like 30% more felt punch than with the st-t2.

This did appear to minimize case damage to only drag marks and no deforming of the rim. I still dont think Id like to reload the cartridges with the damage done.

The only other difference is I used hornaday black 250 grain this time.
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Re: 450 Bushmaster pistol issues.

Postby plant_one » Tue Jun 23, 2020 12:43 pm

if increasing the buffer weight made it feel that much more abusive.. that likely means you buffer is likely bottoming out on the receiver extension with both of them.

does that barrel have a pistol gas port or a carbine? they dont say on their website but from the pic it appears to be a carbine length.


i'm guessing that your best bet is going to be adding on an adjustable gas block and using that in conjunction with a H3 (or heavier) buffer -that will probably resolve both your rim damage issues as well as your felt recoil issues due to your buffer bottoming out.



you gotta remember, a standard a1/a2 rifle buffer is 5.2oz... and a "big bore" buffer for carbine rifle platforms can weight as much as 11oz ( http://heavybuffers.com/reference.html)

many of us are running Hoots CCWS lead slugs in our bcg's to help off set the kind of stuff you're seeing - my 450 is at a little over 9.5 oz of weight between the slug and my h2 buffer in my shared lower.

so just some thoughts to consider. i dont think messing with springs is going to be very helpful. and probably end up causing you more stress than its worth. save those for the 223/556 world where they're known adjusters.
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Re: 450 Bushmaster pistol issues.

Postby androtaker56 » Fri Jun 26, 2020 7:35 pm

Thanks for the reply. I will look into those.
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Re: 450 Bushmaster pistol issues.

Postby androtaker56 » Sat Jul 04, 2020 7:17 pm

I have weighed my options and decided on the rca adjustable gas key. Found it on sale for 21 dollars. My ultimate goal is to use this as a wildlife defense, fishing carry gun in Alaska. So I am tuning it to eventually step up to and only carry 360 grain buffalo bore ammo.
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Re: 450 Bushmaster pistol issues.

Postby androtaker56 » Sun Jul 12, 2020 2:20 pm

It appears that the RCA gas key is working. I still get little extractor markings, but it is not deforming the rim anymore. Recoil is reduced considerably as well. finally shot the 360 grain buffalo bore with no issues.
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