BM Upgrade Suggestions

[Canonshooter]

Hello to all! I am new to this board (but not to ARs or the shooting sports) and would like your collective feedback on some tweaks I am planning for my Bushmaster M4.

Let me start off by saying that I am aware of the limitations of this brand, but I believe that wilth some work it can be improved in terms of reliability. The rifle is a few years old, has a low round count (at this point) and has so far been trouble-free. Since I live in the Peoples' Socialist Republic of New York where we still have an AWB, I need to keep this rifle configured to meet state law. Pictured below is the rifle as currently configured with a Sully stock, Hogue grip, Magpul trigger guard and tritum front post;

http://www.canonshooter.com/photos2/M4-3.jpg

My goal is to retain its KISS configuration for recreational use but make some improvements/tweaks to enhance it's long-term reliability. Here is what I plan on doing - please feel free to comment and offer other suggestions;

1. Better staking of gas key
2. Install mil-spec receiver extension and stake
3. Install heavy-duty extractor spring and insert
4. I am also considering the MGI Buffer (http://www.mgimilitary.com/buffer.htm) - is it worth it?
5. Chip McCormick trigger group - any comments on this product (I've been shooting competitively for over 25 years and can make good use of a crisp trigger pull)?

Not related to reliability, but I am also having the AK Concepts FSC556 compensator installed in place of the lame "Izzy brake" that came from the factory (and not indexed perfectly straight as typical of BM QC).

The good news is that I will soon be moving to the "Live Free or Die" state and will invest in a better rifle once I am a resident of NH. For now, I just want to make the BM all it can be - within reason - but I do plan on holding on to it.

Thanks!

Edit - BTW, this rifle is about 3 years old. I purchased the upper direct from BM and the lower (with A2 stock) from a local shop. Finish on both are good/excellent, fit between upper and lower is good. The rifle sighted in with only a very minor windage adjustment (FSB is on staight) and the factory trigger pull is not bad at all (have not measured weight, but it does not feel heavy and it breaks quite cleanly with very minimal take-up). The gas key is staked, but not well. My only complaint so far is the poorly-indexed brake, which will soon be replaced anyway. That said, the more I read the more I believe that mine is a better sample.

[C4IGrant]

1. Better staking of gas key Do this.
2. Install mil-spec receiver extension and stake No need to do this with your stock.
3. Install heavy-duty extractor spring and insert Install a new extractor insert, spring and maybe a Crane O-Ring.
4. I am also considering the MGI Buffer - is it worth it? No need IMHO.
5. Chip McCormick trigger group - any comments on this product (I've been shooting competitively for over 25 years and can make good use of a crisp trigger pull)?That brand is not my favorite, but should work.



C4

[Canonshooter]

That brand is not my favorite, but should work.


Thanks for your input! What trigger would you recommend? The current factory trigger pull is not that bad - something I can certainly live with. My main condern is reliability, so any suggestions on improving both pull and reliability are appreciated.

Also, which buffer spring would you recommend?

[C4IGrant]

Thanks for your input! What trigger would you recommend? The current factory trigger pull is not that bad - something I can certainly live with. My main condern is reliability, so any suggestions on improving both pull and reliability are appreciated.

Also, which buffer spring would you recommend?


IMHO, there are really only two combat rated triggers (other than a standard USGI trigger). They are the KAC and Geissele.

So if your looking for a quality 2 stage trigger that is reliable, look at these two brands.

If you are interested in a more gaming/bench shooting trigger, look at the JP or Timney single stage drop in triggers.


C4

[Heavy Metal]

4. I am also considering the MGI Buffer - is it worth it? No need IMHO.


I am going to have to disagree with Grant on this one. I find these buffers to make a profound difference.

Thay are pricey but you get what you pay for.

My other recommendation would be to consider a pair of M4 peofile handguards.

[Canonshooter]

I am going to have to disagree with Grant on this one. I find these buffers to make a profound difference.

By "profound difference" do you mean in terms of recoil and/or muzzle jump?

[Heavy Metal]

Yes I do.

[Canonshooter]

Yes I do.


OK, thanks - that's good to know.

The other benefit - at least according to MGI - is that the heavier buffer allows a little more time for chamber pressure to drop before extraction begins, thus decreasing some of the stress on the extractor.

BTW, the Sully stock weighs in at 1 pound/2 ounces and is solid, not hollow like the A2 or A1 stocks. This extra weight/mass is also helpful for "recoil reduction" and eliminates all noise from the buffer tube/spring. In combination with the FSC556 brake and Sully stock, I'm thinking the MGI buffer would really tame what little muzzle jump there is and help make fast, accurate hits that much easier.

[toddackerman]

1. Better staking of gas key Do this.
2. Install mil-spec receiver extension and stake No need to do this with your stock.
3. Install heavy-duty extractor spring and insert Install a new extractor insert, spring and maybe a Crane O-Ring.
4. I am also considering the MGI Buffer - is it worth it? No need IMHO.
5. Chip McCormick trigger group - any comments on this product (I've been shooting competitively for over 25 years and can make good use of a crisp trigger pull)?That brand is not my favorite, but should work.



C4

I agree with Grant on everything above. Here is my take on triggers.

You might want to consider the Timney single stage trigger. I have had Timney's in the past on my Bolt Guns, and they have been flawless. The reviews on the forums for the AR trigger have been very positive as well.

My only opinion on the trigger, is that IF it's to be used for Defensive Situations...keep it a one stage trigger so you don't have any screws or other adjustments that can work loose and create a stoppage in the lower. I prefer my factory Bushy trigger to any 2 stage match trigger for this reason, and I have used both. It's not as "Crisp" as the second stage of a 2 stage trigger, but it always resets, never doubles, and the gun goes bang every time.

I will be getting a Timney for my AR in the near future.

YMMV

Tack

[Canonshooter]

I prefer my factory Bushy trigger to any 2 stage match trigger for this reason, and I have used both. It's not as "Crisp" as the second stage of a 2 stage trigger, but it always resets, never doubles, and the gun goes bang every time.

Tack, thanks for the feedback! Even though the trigger on my current BM lower is probably about the best I ever had on any out-of-the-box SA rifle, this is the type of feedback I was looking for. I would gladly spend $$ to make the trigger pull even better, but I do not want to compromise reliability/durability in any way. I'm thinking I will stick with the stock trigger.

[Robb Jensen]

http://www.canonshooter.com/photos2/M4-3.jpg

If this AR is to be used hard for possible self defense or at a training course I'd do the following:

1. Better staking of gas key (I'd replace key with a BCM key and screws and stake with a MOACKS)

2. Install mil-spec receiver extension and stake (Not needed your AR currently, Mil-Spec receiver extenstions are for CAR stocks, your Sully uses a 'entry length' rifle receiver extension which use a CAR buffer and spring)

3. Install heavy-duty extractor spring and insert (I'd get the BCM SOPMOD upgrade kit which includes an extractor, pin, spring, buffer, Crane O-ring and gas rings or better yet replace the bolt with a BCM unit and use your Bushmaster bolt as a backup.)

4. I am also considering the MGI Buffer (http://www.mgimilitary.com/buffer.htm) - is it worth it? (I'd just use an H buffer from CMT and a standard power chrome silicon spring)

5. Chip McCormick trigger group - any comments on this product (I've been shooting competitively for over 25 years and can make good use of a crisp trigger pull)? (McCormick trigger groups are pretty good but they have a tendency to double after awhile, for a 'social' gun I'd run a stock FCG or a Geiselle)

Not related to reliability, but I am also having the AK Concepts FSC556 compensator installed in place of the lame "Izzy brake" that came from the factory (and not indexed perfectly straight as typical of BM QC). (If the FSC556 perm. mounted will make 16" it's a good choice it's a great brake and flash hider).



My opinions are above in blue.

[Canonshooter]

My opinions are above in blue.

Thanks - much appreciated!

What is the difference between the H, H2 and H3 buffers?

http://www.bravocompanyusa.com/AR15-Stocks-s/49.htm

[twl]

OK, thanks - that's good to know.

The other benefit - at least according to MGI - is that the heavier buffer allows a little more time for chamber pressure to drop before extraction begins, thus decreasing some of the stress on the extractor.

BTW, the Sully stock weighs in at 1 pound/2 ounces and is solid, not hollow like the A2 or A1 stocks. This extra weight/mass is also helpful for "recoil reduction" and eliminates all noise from the buffer tube/spring. In combination with the FSC556 brake and Sully stock, I'm thinking the MGI buffer would really tame what little muzzle jump there is and help make fast, accurate hits that much easier.


That is true, and you can get that delayed extraction timing from any of the buffers of a similar mass. In the case of the MGI buffer, that is 7.1 ounces, which is approximately the same mass as a 9mm "B" buffer.

The MGI RRB buffer goes on to provide an active mechanism to cancel and spread-out the recoil impulse that occurs when the moving masses of the buffer and carrier impact the back of the receiver extension(buffer tube).
This reduces felt recoil, and also minimizes muzzle flip.

These recoil reduction and muzzle flip improvements do not occur with simply adding mass to the buffer system. Conservation of momentum states that the same amount of energy will be transferred to the shoulder, whether you use a light fast moving buffer or a slower heavier buffer.
You must actively do something additional to reduce these effects, and the MGI buffer has a mechanism to do that.

Regarding buffer mass, you must balance the mass of the buffer to the gas system in the rifle. Sometimes with a new barrel, the gas port is not sufficiently large enough to drive a heavy buffer reliabily.
So, take that into consideration when selecting buffers.

As the gas port enlarges from erosion, then heavier buffers may come into play, to compensate for the changes in the gas system from erosion of the port.
This is what the MGI buffer was designed to alleviate, and it(or any heavier buffer) can be inserted into the system when the gas system has a large enough port(either made that way, or from erosion) to function reliably. The active recoil-reducing mechanism in the MGI buffer "self-adjusts" to continuing erosion in the gas port to keep things under control over the life of the barrel.

[AR15barrels]

What is the difference between the H, H2 and H3 buffers?

The weight.

http://ar15barrels.com/tech/buffer-construction.jpg

[Robb Jensen]

Randall you forgot the H3, 3 tungsten weights. 5.6oz. ;)

Then there's the Colt X buffer (I think is 8oz)

[AR15barrels]

Randall you forgot the H3, 3 tungsten weights. 5.6oz. ;)

Then there's the Colt X buffer (I think is 8oz)

I did not have those here to take apart and photograph.

The inside of an H3 looks amazingly similar to an H2 with the steel weight being replaced by the tungsten weight. ;)

I'm really interested to see what's inside the X buffer, but I'm not going to buy one just to satisfy my interest...

[Canonshooter]

Great info, thanks! For my application (low round count through the barrel) the H1 buffer should fit the bill?

If I have the resources, I may give the MGI a try...