How to time a trigger

[jackieschmidt]

For me, timing a trigger is about the feel. I hate "cock on close" when chambering a round. I have a method for timing 700 style bolts while maintaining good pin fall but it's not something I would recommend trying without seeing in person to fully understand the mechanics of timing and how it's effected by different parts. Also I wouldn't attempt that job without a good milling machine.

So many variables in accuracy, but timing isn't really one of them. Amount of fp fall, fp spring weights, fp protrusion...yes on accuracy effects. Timing the trigger to eliminate cock on close, not so much.

I had thought about lengthening the cocking cam on the BAT M bolt, which is the best way to increase pin fall and avoid cock on close. But since I had to re position the trigger hanger anyway, I just moved it back to get a full .250 fall, settling on a little cock on close. In other words, I chickened out.

In the picture, that is not the spring I used. As you can see, it is close to coil bind in the static position. I played with several long course wind springs and got it right at 25 pounds of static pressure.

 

[Michael Huebner]

Jackie

Same as BAT - 1144 Fatigue Proof
Pretty sure it’s 28 Rockwell

 

[jackieschmidt]

Jackie

Same as BAT - 1144 Fatigue Proof
Pretty sure it’s 28 Rockwell

I’m surprised.
I was never a fan of using resulphurized steels for high impact parts. But if it works, it works.

Since the actual load in a firing pin is in the longitudinal, not transverse, the free machining qualities exhibited in 1144 Fatigue Proof are probably not a large concern. Test have shown that resulphurized steels, especially the ones with a higher manganese content, do exibit as much as a 40% reduction in ductility when subjected to loads in the transverse.

I actually had some experience with this 4 years ago. One of our shipyard customers had broke a pinion shaft in one of the rotating platform slewing gears. The gear fit was free hanging, the shaft 3 inches in diameter.

They did not want to wait for us to get a piece of 4140 and have it hardenned and tempered to 30 RC for the correct strength levels, so we used a piece of LaSalle 1144 Fatigue Proof.

the shaft failed after around 3 months use. It broke right below the bearing support and the gear hub, which was subjected to a high transverse load.

We then got a proper piece of 4140, roughed it out, then had it heat treated to 30RC. It has been running since.

 

[Michael Huebner]

I’m surprised.
I was never a fan of using resulphurized steels for high impact parts. But if it works, it works.

Since the actual load in a firing pin is in the longitudinal, not transverse, the free machining qualities exhibited in 1144 Fatigue Proof are probably not a large concern. Test have shown that resulphurized steels, especially the ones with a higher manganese content, do exibit as much as a 40% reduction in ductility when subjected to loads in the transverse.

I actually had some experience with this 4 years ago. One of our shipyard customers had broke a pinion shaft in one of the rotating platform slewing gears. The gear fit was free hanging, the shaft 3 inches in diameter.

They did not want to wait for us to get a piece of 4140 and have it hardenned and tempered to 30 RC for the correct strength levels, so we used a piece of LaSalle 1144 Fatigue Proof.

the shaft failed after around 3 months use. It broke right below the bearing support and the gear hub, which was subjected to a high transverse load.

We then got a proper piece of 4140, roughed it out, then had it heat treated to 30RC. It has been running since.

Jackie,

I trust and believe what you are saying as I am not a machinist and have read all your posts.
I just wanted to use what BAT use https://www.batmachine.com/faqs/
You will see they say firing pins 1144 fatigue proof. You would have to ask Bruce why they use this steel.
Cheers

Michael

 

[Ledd Slinger]

The BAT HR and a Bixn Andy TacSport Pro is a match made in heaven. It's the only receiver/trigger combo I've ever owned personally that has 'drop-in ready' perfect timing and still good FP fall. Memory is a little fuzzy so would have to measure again to be sure, but I think it has .248" pin fall and zero cock/over-cock on close. Pin the BnA into the receiver and done. Nothing else needed.

 

[jackieschmidt]

Jackie,

I trust and believe what you are saying as I am not a machinist and have read all your posts.
I just wanted to use what BAT use https://www.batmachine.com/faqs/
You will see they say firing pins 1144 fatigue proof. You would have to ask Bruce why they use this steel.
Cheers

Michael

Steels like Stress Proof, Fatigue Proof, and ETD 150 have been around for years. They were brought out by LaSalle Steel as alternatives to steels that require a hardening and tempering procedure to reach desired properties of tensile, yield, and ductility.

Stress Proof and Fatigue Proof offer the added free machining aspect.

This is why they are popular in the manufacturing of certain parts, in this case, firing pins. While they might not be the best choice, it is totally adequate, especially considering the savings in time and manufacturing tooling cost due to it’s free machining qualities.

I feel the same way about action bodies. Multitudes of manufacturers use 416 stainless, taking advantage of its free machining qualities. While not nearly as strong in all aspects as properly age hardenned 17-4 or properly heat treated Chrome Moly, it seems to be adequate for the task at hand.

 

[VA_XTC_Shooter]

In Hambly's Centerfire Rifle Accuracy book, he states timing the trigger to engage the sear properly can be done by removing material from the cocking piece face, maintain the same angle, just remove the amount the sear is out.

I recommend his book, it is great.

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