Hornady O.A.L. Gauge - inconsistent readings

[radford56]

While I've reloaded quite a bit for AR-15s, I've mostly loaded magazine length bullets.

I have some 80 grain Sierras that I'm planning to load for my Wylde chambered AR-15. I know the OAL listed in the Sierra manual (2.550) is way too long for my chamber. From what I've read, OAL around 2.470-2.475 is probably about right for the Wylde chamber with the 80 grain SMK (but you have bullet tip inconsistencies to account for), but I wanted to get a good reading using the Hornady O.A.L. gauge. I have a straight gauge that I've always used and it works great on my bolt rifles. I couldn't get a consistent reading with it in the AR-15 so I went out and bought the curved gauge - which I was told is more accurate for the AR-15 - and tried it. Readings are all over the place even though I'm trying to be as consistent as I possibly can be.

So I'm wondering what I'm doing wrong. Am I the only one who can't get a good measurement using these gauges on an AR-15?

Should I just punt and try to load around 2.470 COAL?

 

[DngBat7]

Funny you should ask this, I just got off the phone with Sierra with the same exact question for 300blk. They told me to clean my chamber and check sever times with the Hornady gauge. He said I really should not go more than .020 below their listed coal. Or it could really mess with the pressures. He also said try skipping the Hornady gauge, make a dummy round with no primer or powder at their recommended coal, chamber it and see if it comes out with marks from the lands on it.

 

[Milo 2.0]

Is this a unfired chamber? Sometimes on new chambers, bolt guns, readings are sporadic, I fire 10-12 rds and redo. Get better readings.
If you make 10 tries, and the same number comes up 4-5 times, I'd roll with it, I'm assuming you will fine tune seat depth after this, making it just a number.

 

[Just Dave]

I get best results when i tip the barrel down, let the bullets own weight determine where it stops, not your sense of feeling ( which can vary greatly, )

 

[Howland]

I got the same thing with an unfired chamber, 65 thou difference between longest and shortest. Even the shortest CBTO exceeds mag length and I don't want to have to single feed, but I'll try the suggestions offered because I want to know how much I'm jumping, even if it is only academic.

 

[radford56]

Are you single feeding?
2.4" wont fit in magazine, I windowed the front of one of my magazines loading for 6x45 gas gun. I can load out to 2.37 with it.
Tips run up the channel of mag well.

Yeah, I'm single feeding the 80 grain SMKs. I had a dummy round that was loaded to 2.550 as specified in Sierra's manual. When I tried chambering it, the bullet stuck in the rifling and I pulled the bullet out of the case when I tried to extract it. So obviously 2.550 is too long for my chamber!

I checked a couple of references - Zediker's book for one - that recommend seating the 80 grain SMK somewhere around 2.470 for a Wylde chamber.

The rifle has around 1K rounds through it, all mag length. I was just trying to get a good measurement by using the Hornady gauge before i start loading 80 grainers for this rifle. As stated, I can't get anything consistent with either version of the gauge.

 

[mchees1]

I used some Starret M1 spray lube so the cable slides easier through the bend on my curved Hornady OAL gauge. It does help me have a better feel for when the bullet is touching the lands. I have had a few rifles, both bolt and AR-15 style, that I couldn't get a good feel for or consistent lengths. I have found that there was a little roughness at the end of the chamber just before the lands that interfered with the bullet - the bullet would drag on the rough spots so it was hard to tell when I actually hit the lands. I discovered this by using a sharpie to coat the bullets. When I got the bullets out of the chamber I could see scratches on the sharpie ink. Then I used my Lyman borescope and saw the ink on the rough surfaces before the lands. What I end up doing is to go ahead and use more force and make sure the bullets are jammed in the lands, not just stopping at the friction from the rough spots. If I can repeat the length while firmly jamming the bullets, I then just guess as to how many thousands to subtract to get a normal length to the lands. Not really accurate, but it has worked for me. I usually subtract about 0.010 and test some loads from there.

 

[Barlow]

I used some Starret M1 spray lube so the cable slides easier through the bend on my curved Hornady OAL gauge. It does help me have a better feel for when the bullet is touching the lands. I have had a few rifles, both bolt and AR-15 style, that I couldn't get a good feel for or consistent lengths. I have found that there was a little roughness at the end of the chamber just before the lands that interfered with the bullet - the bullet would drag on the rough spots so it was hard to tell when I actually hit the lands. I discovered this by using a sharpie to coat the bullets. When I got the bullets out of the chamber I could see scratches on the sharpie ink. Then I used my Lyman borescope and saw the ink on the rough surfaces before the lands. What I end up doing is to go ahead and use more force and make sure the bullets are jammed in the lands, not just stopping at the friction from the rough spots. If I can repeat the length while firmly jamming the bullets, I then just guess as to how many thousands to subtract to get a normal length to the lands. Not really accurate, but it has worked for me. I usually subtract about 0.010 and test some loads from there.

I have had the same experience. Use a HARD jam and average 5 bullets, then back off .010 or .020. Barlow