Trigger work on Bushmaster 97 ?

[TMan]

The Bushmaster 97 pistol is basically a sawed off AR-15. It's lower receiver parts are identical to those in the AR-15.

I absolutely hated the trigger on it. It had creep, it was heavy, and gritty. I bought Robert Dunlop's DVD on AR-15 trigger work, and I'm pretty much satisfied. It is still more positive than it needs be, but doing more stoning on it is way down on my priority list.

I recently bought Patrick Sweeney's book on Gunsmithing Rifles. ISBN 0-87341-665-1 On page 69 he states:

The trigger parts are surface-hardened for durability. If you stone the engagement surfaces you can and will break through the hard skin and expose the relatively softer steel underneath. If you stone, the trigger job you sweated over will not last long. Do not polish or stone your AR hammer or trigger in an attempt to improve your trigger pull. Even apparent success can be soon followed by disappointment.

So, I'm ready to put sugar in Mr. Dunlop's Simple Green. Why would they sell a DVD on doing a trigger job, when the results wouldn't last? Or, is he talking about the early Colt AR-15's and they don't do that anymore?

I've been home sick with a stomach problem all day, and this isn't helping.

[MLB]

If the trigger group parts are surface hardened, stoning them would likely remove this hardened layer as its only a few thousandths thick. If the entire part was hardened though, should be no problem. Hard to tell.

Hardening, Tempering, and Annealing are topics that have always interested me, but have never learned well. I'll have to remedy that.

As I understand it, a metal has an intrinsic hardness (resistance to deformation, and therefore abrasion) that can be modified either throughout the metal (hardening and annealing), or at the surface (case hardening, or carborising).

The following link is an interesting summary of these processes. I may have to try a few...

easyweb.easynet.co.uk/~chrish/t-ht.htm

[MLB]

"Hard to tell."



I can't help myself...

[TMan]

mlb said:

"Hard to tell."

Just remember: we all have guns. ;D

(Great smiley face by the way. I'm stealing it.)

[somery]

["DoubleAction"]

TMan; It's always good to know something about the steel used in the trigger group before removing any metal from it's surface. I sometimes avoid the issue altogether by replacing the factory trigger components, which is far more expensive than working with what I have.
There are plenty of trigger components available through Brownell's for the AR-15 rifles, as you already know. Wilson Combat uses the adjustable JP trigger unit in their rifles, and it is very good; You can also order a match trigger from Bushmaster or Armalite.
Robert Dunlap might have been referring to the Colts. Those people who shoot in the Civilian Marksmanship Program, Colt Cup Rifle Matches, and Service Rifle Championships have alot of information on honing certain triggers manufactured for the AR-15 rifles.

[TMan]

I got the bright idea (obvious to others, bright to me) of contacting Bushmaster to see what they had to say about the subject. It was a good response, but not what I was hoping for:

All manufacturers AR15 triggers are case hardened.
Subject: Trigger pull

The standard triggers are designed for 5.5 to 9.5 pounds. You can reduce the pull a couple of ways.
One is to polish the front of the trigger with some 800 grit wet & dry paper. Do not remove any more material than necessary as it should only be polished. If too much material is removed you can cut through the case hardening and the trigger will fail. I use a piece of glass for a flat surface using light gun oil or kerosene. Do not change any angles or round over corners. Bend the hammer spring doglegs from the standard 180 degrees to about 120 degrees by wrapping the coils of the spring in the same direction they are now. Use Tetra grease or Moly-Slide to lube the sear surfaces. That should bring it down to 4 to 5 pounds.
The other way is to order the competition trigger part number 8448592-SCG for $45.00 and the competition hammer spring part number 4349008 for $1.99. The competition trigger has a different angle on the front that is highly polished already. The new angle drops straight off the hammer without negative pull. You will notice that when you pull the trigger with the standard parts that the hammer moves backward before being released. The competition hammer spring is prebent to the 120 degrees as mentioned above. With Moly-Slide lubricant the trigger pull would be 3 to 4 pounds.


Thank you,
Jim Eden, Tech Support

I don't remember what I paid for the Bushmaster, but I think it was close to $1000. I would have been willing to pay $1047. Looking at MidwayUSA and Brownells, there are a lot of aftermarket triggers available, but I think I'll spend the $47, which is 1/4 that of a Jewel, and put it in to replace the one I've already screwed up.

There isn't any way of conveniently case hardening it now that I've destroyed the outer level, is there?

[MLB]

Well, convienient is a relative term, but there is some discussion on how to case harden metal on the link in my post of 9/20.

[TMan]

Thanks MLB, I knew I'd read something, but forgot where I read it. I had a hard time getting to the site, but it finally connected.

Of course reading the article brings more questions:

1) Do you think the trigger will be a low-carbon steel? If so, I think I'll order Kasenite from Brownells and try with that.

2) I'm thinking that from a heating standpoint that heating it to a temperature suitable for chisels and punches i.e. purple blue would be sufficient. I have no idea what the scale of Vickers converts to in F⁰

3) Would purple-blue be hotter than "red-hot"? He doesn't show a complete scale. Would I be able to heat a small part to purple blue with just a mapp gas torch?