C.O.L. for semi-auto

[Pheroze]

Is there a method to determine the best C.O.L. for a semi-auto rifle? For my bolt guns I use the method of chambering a dummy round to find the chamber size then adjust as required. Can you do a similar technique by letting the bolt close with a semi?

 

[BRICKBURN]

It only makes sense to me.
Closed is closed, no matter what action.

Maybe someone else knows something that I don't.

 

[sestoppelman]

To be safe I go by SAAMI specs. As in .308 - 2.8" or a tad under.

 

[Pheroze]

Ok thanks guys!

 

[greyfox]

Usually limited by mag box and action cycle.
Run dummy rounds to the lands then back off maybe 5/1000's (assuming you reload??) action closes tight without a hang up, then make 3 rounds tot he same specs and cycle them through. Make sure they fit the mag and feed/load properly.

 

[Pheroze]

Hi greyfox,

When you run the dummy round through do you allow the bolt to close with full force or do you ease the bolt on them? I was concerned the force of the closing bolt would force the bulet into the lands too aggressively.

With a bolt action I seat the bullets approximately 0.020 back from the lands as a starting point. With the semi are you suggesting seating the bullet 0.005 back from the lands as a starting point and then adjust to fit the mag box and then shorten if they do not chamber?

Thanks for the input.

 

[lcq]

To be safe I go by SAAMI specs. As in .308 - 2.8" or a tad under.

Agreed. Hornady makes an OAL gauge http://www.hornady.com/store/OAL-Gauges/ for autoloaders. Even though you are generally limited by mag length I would either measure it or follow sestoppelman's advice and go SAAMI and be safe.

 

[greyfox]

NEVER ride the bolt close, semi-autos (and autos) function with full power loads and are designed to close fast and hard!
90% of the autos I get with "The gun won't shoot" are because someone rides the bolt closed, Let it slam: it's how it operates, how it was designed. The other 10% is wrong ammo!!!
Other issue. back off 10/1000 if it makes you feel better make some dummy rounds run the bolt all the way back and let her fly. If the bullet gets stuck in the throat (not likely) a simple rod tap from the front (muzzle) will clear it and you'll know to crimp (lightly).
Personally, I smoke (soot) a bullet, run it to lande contact, then back off 1/4 turn in the die, - back off the landes so 1/4 trn in on the seating die - Measure, try it, adjust as necessary.

NOW for hunting. SAAMI specs and full length resize, not going to take a chance on a hunt and I don' t shoot over 300 yds, to me that's sniping, not hunting, but that's a personal preference.

So, to your original question, same as a bolt for seating but when checking cycling and function let the bolt loose - that's how it's going to operate when the rounds are live.

 

[Pheroze]

SAAMI specs it is! I load to shoot alot so I can hunt better. And to use a variety of premium bullets. My preference is at ranges less than 300 yards. Actually, less than 100 is better.

Question: if the semi-auto is designed to operate at full loads do you build a load differently? What I mean is, do you start somewhere above starting loads or risk not having the action operate properly?

 

[greyfox]

Personally, I don't start at starting loads, I go back about 5% of maximum and that's where I start.
What rifle are we talking about here?
If it's gas operated, it has to have the power to unlock the bolt then the gas to cycle it, aa recoil operated has to have the power to cycle the action. Shooting reduced loads probably ain't gonna get her working!!!

 

[Pheroze]

My father has two Brownings semi-autos in 270 win and 7mm RM. I like the idea of backing off max 5% because it sure takes a while otherwise. lol I noticed Hornady especially has light start loads.

 

[lcq]

SAAMI specs it is! I load to shoot alot so I can hunt better. And to use a variety of premium bullets. My preference is at ranges less than 300 yards. Actually, less than 100 is better.

Question: if the semi-auto is designed to operate at full loads do you build a load differently? What I mean is, do you start somewhere above starting loads or risk not having the action operate properly?

Another consideration is powder. Autoloaders do very poorly with slow powders where a bolt can use fast or slow. If I were shooting my 3006 Rem 7400 I would use H4895 or Varget but not IMR4350 or H4831 they are too slow

 

[greyfox]

My father has two Brownings semi-autos in 270 win and 7mm RM. I like the idea of backing off max 5% because it sure takes a while otherwise. lol I noticed Hornady especially has light start loads.

With the 270 and 7mm Rem Mag in a BAR the mag box will dictate the maximum overall length

 

[ZG47]

Pheroze
Treat the CIP/SAAMI overall length as your maximum and ... always CRIMP your BULLETS to the case.

A jam is bad enough but if a bullet actually slips out and then gets pushed into the rifling by another round, things will get exciting.

Years ago our forest service started supplying some of it's 'cullers' with Ruger Mini 14s. They also decided to economise by getting a local importer of ammunition and components to load some ammo for them. There were a number of barrel failures with those rifles. The ammo supplier consulted a gunsmith friend of mine, recently deceased, who advised him to crimp the projectiles. He did this, on the quiet, and the problem disappeared.

 

[lcq]

Pheroze
Treat the CIP/SAAMI overall length as your maximum and ... always CRIMP your BULLETS to the case.

A jam is bad enough but if a bullet actually slips out and then gets pushed into the rifling by another round, things will get exciting.

Years ago our forest service started supplying some of it's 'cullers' with Ruger Mini 14s. They also decided to economise by getting a local importer of ammunition and components to load some ammo for them. There were a number of barrel failures with those rifles. The ammo supplier consulted a gunsmith friend of mine, recently deceased, who advised him to crimp the projectiles. He did this, on the quiet, and the problem disappeared.

Lee makes a couple of really good products and the "factory crimp" is outstanding

 

[Rob404]

I recently picked up a Ruger 44mag Autoloader Carbine,,I thought it would a great Hog Gun, The first time out the rifle jammed constantly,I was using some factory ammo that turned out had 9gr of powder, when I Re-loaded my own with 24Gr of IMR 4227 the Rifle functioned perfectly,I'd like to try some H110 but can't seem to find any right now

 

[Pheroze]

9gr?? I am not familiar with the load data for that cartridge but was it loaded in error by the factory?

 

[Rob404]

9gr?? I am not familiar with the load data for that cartridge but was it loaded in error by the factory?

It was Blazer Pistol Ammo, Maybe plenty of powder for a handgun, or even a spring operated semi but the Ruger is Gas Operated

 

[ZG47]

Rob44

W296 is the same propellant as H110. Any differences are purely batch related.

 

[Rob404]

Rob44

W296 is the same propellant as H110. Any differences are purely batch related.

Thanks I'll look around for some W296