6.5 CM Load for AR with H4350 or Varget

[EdHarley]

"I want to keep the pressure proper for a gas gun."

Do you run an adjustable gas block? If not get one or you will more than likely be over gassing you gun.

Yes I have an adjustable gas block. I messed with it a bit last time I was out. Adjusted it to the factory load and worked up my ladder figuring the factory load with Prime Ammo would be as fast as I would go initially. Most of the lower charge loads did not cycle the action so it wasn't too hot. The loads >2600 cycled properly. Have you seen velocity changes by adjusting the gas block?

 

[EdHarley]

Had a few problems with the 140 SMK. I based the COAL on magazine length, ~2.8" and then based the base to ogive length of the round on the COAL. This turned out to be much too long. Had the bullets jammed into the barrel. After a misfire and a stuck bullet with powder in the chamber. I checked the chamber length with that bullet and the Hornady tool and redid the seating depth. The best load prior to that was 140SMK, H4350 at 41.2gn, Fed 205M, vel of 2630 with SD of 3 and ES of 6. Waiting to see what the shorter rounds will do.

 

[EdHarley]

I

Start at 40 and work your way up, until you see pressure signs.
Adjust your gas block as needed.
I’m shooting 140 ELDs.
I am at 42+ grains

I just got a large container of RL 16 to try in the CM and for a 6XC bolt gun. If you are adjusting the gas block to minimize pressure are you still seeing ejector marks as pressure signs or primer flow or what?

 

[Earnhardt]

Using the adjustable gas block to fine tune the BCG, and JP-SCS buffer

I have a titanium BCG, (12 oz.) so I need less gas than a standard BCG (18 oz.), but with AR10’s/LR308’s an adjustable gas block is almost a must when reloading

 

[EdHarley]

Using the adjustable gas block to fine tune the BCG, and JP-SCS buffer

I have a titanium BCG, (12 oz.) so I need less gas than a standard BCG (18 oz.), but with AR10’s/LR308’s an adjustable gas block is almost a must when reloading

I have the gas block but am wondering how close I can get to the pressures in a bolt gun. I can keep adjusting it to minimize pressure but there will be a point where the pressure increases too much. What I wanted to know was where will I see the pressure signs? extractor marks, or signs on the primers?

 

[Hoot]

I have the gas block but am wondering how close I can get to the pressures in a bolt gun. I can keep adjusting it to minimize pressure but there will be a point where the pressure increases too much. What I wanted to know was where will I see the pressure signs? extractor marks, or signs on the primers?

The most reliable sign of adverse pressure in an AR platform is Case Head Growth. With hot loads, its not unheard of to see .001-.0015 CHG. More that that is borrowed time.

Hoot

 

[EdHarley]

Thank you Hoot. You just take a caliper to the range then?

FYI, I have been reading your other posts on the 6XC with interest. I just got a new 6XC and was going to get a set of dies when I decide Tubb vs. Redding.

 

[Hoot]

Thank you Hoot. You just take a caliper to the range then?

FYI, I have been reading your other posts on the 6XC with interest. I just got a new 6XC and was going to get a set of dies when I decide Tubb vs. Redding.

I prefer to sort my AR brass with a micrometer but yeah a caliper will do. This is an important however: Measure a few cases before you shoot so that you have a baseline to compare the fired cases to. CHG will happen. You are mainly concerned with excessive after firing. That's the sign of a risky recipe. Swipes are more often a sign of a timing issue but excessive pressure can cause them as well. Flattened primers are either loose pockets or excessive pressure but CHG growth will manifest before you flatten primers out of good pockets.

I sort my deprimed, cleaned, resized AR brass into quart peanut butter jars by CHG. +.0005,+.001, +.0015, etc for each caliber, up to the size that will no longer drop into the chamber unassisted. AKA Thunk Test. Beyond that dimension, they are relegated to the scrap bin. Unless you have a "loosey goosey" chamber, you rarely see one that will take CHG of .002.

Hoot

 

[EdHarley]

I prefer to sort my AR brass with a micrometer but yeah a caliper will do. This is an important however: Measure a few cases before you shoot so that you have a baseline to compare the fired cases to. CHG will happen. You are mainly concerned with excessive after firing. That's the sign of a risky recipe. Swipes are more often a sign of a timing issue but excessive pressure can cause them as well. Flattened primers are either loose pockets or excessive pressure but CHG growth will manifest before you flatten primers out of good pockets.

I sort my deprimed, cleaned, resized AR brass into quart peanut butter jars by CHG. +.0005,+.001, +.0015, etc for each caliber, up to the size that will no longer drop into the chamber unassisted. AKA Thunk Test. Beyond that dimension, they are relegated to the scrap bin. Unless you have a "loosey goosey" chamber, you rarely see one that will take CHG of .002.

Hoot

Will do, thank you.

 

[Old Navy]

ARs are over gased is a very broad term when you consider all the makes, models, calibers etc. I fell for that adjustable gas block for my perfectly fine Aero Precision 6.5 CM. Got it adjusted great for 140 VLDs using H4350 and switched over to some 130 with Varget and no cigar. Back and forth we went. It is now just another relic in my gun room.

 

[EdHarley]

So did you just go back to the 140?