Question about parts upgrade

[magsig]

Hello, I'm new here so please don't take my question the wrong way. I'm not trying to be a jerk...I'm just looking for opinions. I have a 3rd tier rifle (BM XM-15) and I would like to know what exactly is wrong with Bushmaster rifles. I understand that there have been some issues with these rifles and I would like to know which parts I might need to replace in the future. The main components (upper, lower, barrel) seem to be quality parts...so can I just replace the bolt, bolt carrier, fire control parts and springs to get a decent rifle? I'm not an operator or HSLD guy...just want something I don't have to worry about. I also have what some refer to as a tier 1 rifle (colt 6721). Can I bring the bushy up to the Colt's level? Am I missing anything else? Are there other issues besides parts that I should be aware of? Thanks in advance for your help.
Magsig

[baffle Stack]

The carrier should be fine, just give it a good stalking job on the gas key. I would say buy another bolt (MP tested) and keep that around just incase you break the BM bolt.

If you have a flattop you may want to buy that taller front sight post from BM.

If it's a carbine and you want to upgrade your stock, I would recommend looking at the Magpul ctr. They make a version that will fit the BM receiver extension. If you go with another brand like Vltor you'll have to replace the extension and spend more money doing so.

There are a lot of other odds and end you could change in order to bring it up it damn near tier 1 quality, but I think the bolt and the key stalking are the big ones. There are a lot of people that might say you need M4 feedramps, H buffer, etc etc, but if your gun shoots well without these...then shoot the crap out of it till you feel you need the upgrades. Which I imagine would be many thousands of rounds into the future. :cool:

[C4IGrant]

Hello, I'm new here so please don't take my question the wrong way. I'm not trying to be a jerk...I'm just looking for opinions. I have a 3rd tier rifle (BM XM-15) and I would like to know what exactly is wrong with Bushmaster rifles. I understand that there have been some issues with these rifles and I would like to know which parts I might need to replace in the future. The main components (upper, lower, barrel) seem to be quality parts...so can I just replace the bolt, bolt carrier, fire control parts and springs to get a decent rifle? I'm not an operator or HSLD guy...just want something I don't have to worry about. I also have what some refer to as a tier 1 rifle (colt 6721). Can I bring the bushy up to the Colt's level? Am I missing anything else? Are there other issues besides parts that I should be aware of? Thanks in advance for your help.
Magsig

If your BM is a range gun (not used for self defense), just leave it as it until something breaks.

If you want to upgrade some things then start with these items:

MP tested bolt (black insert, Crane O-Ring)
H or H2 buffer
CS buffer Spring


These simple upgrades can and will make a world of difference in reliability.


C4

[magsig]

Thanks for the suggestions. I'll definately keep those parts in mind.

[baffle Stack]

If your BM is a range gun (not used for self defense), just leave it as it until something breaks.

If you want to upgrade some things then start with these items:

MP tested bolt (black insert, Crane O-Ring)
H or H2 buffer
CS buffer Spring


These simple upgrades can and will make a world of difference in reliability.


C4

I like the way this guy thinks. Good advice Grant.

[C4IGrant]

I like the way this guy thinks. Good advice Grant.

Thanks. No need to change out a part on a gun that is running (as long as it is not his "go to" weapon).

Not all dealers are blood sucking vampires and most of the good ones (which are on this forum) have been known to talk people out of gear from time to time. ;)




C4

[Diz]

I have the same BM carbine that you have. I would suggest upgrading in phases. Here's what I did.
Phase 1: Pretty much what Grant suggested:
CMT Bolt, MPI'd, with HD ejector spring, black insert, and Crane O-ring
Proper BC/keyway staking
CMT H-2 Buffer w/ ISMI spring
CMT lower parts kit
CMT charging handle w/ BO Gen II tac latch
Ergo grip
MP trigger guard

Phase 2:
BCM upper, 14.5" M-4 profile w/YHM FS
USGI Side Sling Swivel
MI BUIS

Phase 3:
EOTech or Optic of your choice

Phase 4:
MI #17 Rails with MP or covers of choice
VFG as required
Light and mount of choice

Phase 5:
Vltor modstock and buffer tube ass'y

This is a mildly custom build but within reach if you do it in phases.
I think this build is roughly equivalent to a "tier 1" weapon. As I ring it out in the coming months I will report back.

As to your question, why is BM considered sub-par; well the biggest reason is the poor track record of BM bolts in carbines; they have a tendency to crack and break at the cam pin hole and/or locking lugs. A good rule of thumb is to replace your bolt every 5,000 rds; a CMT bolt can do this easily, a BM may or may not. Then there is the bore and chamber. BM chambers tend to be tight, which is good if you are a varmint hunter, but bad if you want to shoot any surplus 5.56. Their bores are 1-9 for the most part; 1-7 is preferrable for heavier weight bullets, such as the 77 gr which has proven to work so well. The front sight bases are all "A-2", which are approx. .060" LOW, meaning your BUIS on your flat-top upper will not line up with your front sight, without over-extending the front sight. You can go with an extended front sight but I thought it looked like shit. I even e-mailed BM and asked them if they would install a new "F" marked front sight base and they responded that they don't make them. Then there's the buffer tube. It's not mil-spec, so to run a Vltor or Crane stock you gotta replace the whole damn ass'y. And finally, when I replaced the lower parts, the trigger was much crisper, and the selector switch was also tighter, so I'd have to say these CMT parts are also superior to BM. In all fairness, I have have shot a couple of thousand rounds through my Bushy, and it never shit the bed, however, I have heard enough anectodal evidence from others in the biz, whom I trust, that I consider it wise to upgrade a stock BM carbine with phase 1 parts at a bare minimum. The rest is up to you.

[magsig]

DIZ and all others,
Thanks for your help. I think I will replace the bolt, carrier, buffer, springs and lower rec. parts. I don't care about optics or BUIS because to me it's just a simple, close range carbine(11.5/5.5). Besides the upper is A2. I just want it to go bang everytime. Thanks again, magsig

[Cold Zero]

Magsig;

the advice given above is worth following.

I have the same rifle with around 12,000+ rounds thru it. I am still running the original B.M. bolt and bolt carrier, which has been properly staked. The extractor has been changed once and has the arm forte defender d ring. The buffer spring is still the original and it has compressed, i check it periodically.

I did have to send the rifle back when I first got it for an improperly indexed front sight tower and defective barrel. Both of which were promptly replaced and the rifle has run like a sewing machine ever since. I think I got a good one. I expect to start experienceing problems shortly. Time for some p.m..

make the necessary upgrades to ensure reliability and enjoy your new rifle.;)

[svtar15]

Just take care of the one you've got. I'm sure you've heard the expression,"If it ain't broke, don't fix it." Just because Colt did it doesn't make it the only way to do it. The classification of "Tiers" is subjective to who it is telling the story. I would consider BM a Tier 2 weapon, not 3. But, experts are a dime a dozen on these websites. The advice Grant gave you is the best on this thread.

[C4IGrant]

Just take care of the one you've got. I'm sure you've heard the expression,"If it ain't broke, don't fix it." Just because Colt did it doesn't make it the only way to do it. The classification of "Tiers" is subjective to who it is telling the story. I would consider BM a Tier 2 weapon, not 3. But, experts are a dime a dozen on these websites. The advice Grant gave you is the best on this thread.


Its not really about Colt or FN, it is about having the official TDP and following it. The Tiers thing (as I said) is my opinion and BM is a tier 3 IMHO because we have seen more broken bolts from this company than any other.



C4

[magsig]

OK...so I'm gonna replace the bolt with the CMT MPI'd one mentioned...How do I headspace it? Do I need to send it to a smith?

[C4IGrant]

OK...so I'm gonna replace the bolt with the CMT MPI'd one mentioned...How do I headspace it? Do I need to send it to a smith?

Getting a bolt checked for headspace is a good idea, but don't think it is 100% neccessary in this case.


C4

[Diz]

The easiest way to do this is with a GO/NO GO gage set. Available from Brownells and others. They run about $50.00. You simply put these round-shaped check gages into the chamber and attempt to close the bolt over them. The GO gage should close (i.e., the locking lugs should fully turn); the NO GO gage should not. A quick and easy check for proper head-spacing. If you do not want to buy them, then take it to a good 'smith and see what he will charge to do this for you. AR headspace adjustment is pretty much beyond the range of the hobby workshop; for us the only thing you can do is swap out bolts until the proper headspace is reached. FWIW, I've never had a bolt and chamber combination that would not head space correctly, so this shouldn't be an issue. But I always check head space anyway; just a good habit.