Need help with comparator OAL

Ray HP · July 3, 2002, 07:58 PM

I am preparing to reload for the first time in the 223 variety for 2 AR-15's (DPMS & Armalite). I checked both chambers using a Stoney Point OAL Gauge and bullet comparitor with Hornady 75g HPBT bullets.

Now for my problem and confusion. I measured each rifle with the same 5 bullets. The DPMS measures 2.969+/-0.001, the Armalite measures 2.860 with 2 bullets and the remaining 3 bullets at 2.851, 2.855 and 2.856. These are actual vernier measurements with the comparitor attachment that is 1 inch long.

My questions are:
1) Is throat variation from brand to brand as large as 0.1 that I measured? It seems like the DPMS has a very long throat.

2) Why does the Armalite give 2 sets of measurement groups?

3) If I set the length at 0.020 from the lands the OAL will be to long for the DPMS. Do I settle for the longest length that will fit the mag?

The DPMS has about 1000 rounds and Armalite about 400 rounds through each.

Thanks in advance for the help.

Ray

444 · July 3, 2002, 08:18 PM

Ray, I can't answer your questions, but I would like to chime in here and say that I would also like some advice on using the Stoney Point tool. I can't get consistent measurements either. I am sure it is because there is something I am doing wrong; obviously the chamber isn't changing dimensions between readings. I have tried using a different bullet each time in case I deformed the bullet in some way etc, yet no two readings are the same.

Help !!!! Two guys looking for answers.

Dave P · July 5, 2002, 01:09 PM

1) Is throat variation from brand to brand as large as 0.1 that I measured? It seems like the DPMS has a very long throat.

Yes every rifle is different; there is no standard for the throat that I know. If you have a stock rem 700, the bullets normally cannot touch the lands, they are out there so far!

2) Why does the Armalite give 2 sets of measurement groups?

Beats me, but that repeatability (+/- 5 mil) is about what I see with a smoked bullet/split case method. I need someone to prove to me that they can accurately measure seating depth (repeatably) to a couple of mil! I say, don't sweat it!

3) If I set the length at 0.020 from the lands the OAL will be to long for the DPMS. Do I settle for the longest length that will fit the mag?

If you are loading for accuracy, load for each rifle individually, and don't use a magazine.

NoSweat · July 6, 2002, 12:14 AM

I had some problems measuring with the Stoney Point when I first tried it. The secret is to TAP the rod to push the bullet firmly into the rifling.

If you push it in gently, you will get erratic readings.
A good firm tap ( done consistantly) on the rod before tightening the thumbscrew will give consistant readings on your caliper.

I have also used the RCBS Precision Mic. It will give consistent readings but the number differs from that on the Stoney point. I have stayed with the Stony point as it is easier to use. I check every 5 or 10 rounds to see if the seating is changing. It WILL CHANGE if you use a different lot of bullets.

444 · July 6, 2002, 06:37 AM

This may sound silly, but what do you mean specifically by "tapping". When I was doing this, I took my index finger and tapped on the end of the rod. I tried to use the same amount of force and tap it the same amount of times. I really went out of my way to be consistent in every aspect but obviously, I was not consistent enough. If you were getting good, consistent readings, please describe in detail, your method.

rick_reno · July 6, 2002, 10:05 AM

I've had the same problem you're havng with this thing. For me it works the way I think it's supposed to work on some guns, on others I also get different measurements regardless of how many times I attempt to measure it. I shoot a lot of Sako rifles and this tool works great on a 30-06, but I've got a heavy barreled 308 that I've never been able to get the same measurement twice on. A suggestion that might help you is to tap (use a small plastic hammer) on the sliding piece until the bullet sticks in the lands, set the screw and push the bullet out from the muzzle with a cleaning rod. I don't know if that'll help with the end result you're trying to obtain, but it should give you consistent numbers.

NoSweat · July 6, 2002, 03:44 PM

444.... I forgot to mention one thing. Don't let the bullet in the case touch the rifling before you tap it into place. I won't call it "slamming" the bullet into the rifling, but a tiny slam, or a tap to send it home is what I use. Yes I use my finger for this.

I got this technique from a buddy who said he got it from Sierra.

The actual measurement is really not that important. You still have to load a series of Overall Lengths, and test fire them to find the best OAL for your rifle.

I recently did this with a Hart barreled Rem 700 in 22-250, and was using a Sierra # 1410 52gr HPBT. I found the most accurate position was about .010 off the lands. I then tried some Sierra # 1400 53gr HPFB, and it also shot the best at .010 off the lands.

July 3, 2002, 07:58 PM	#1
Ray HP Member Join Date: July 7, 2000 Posts: 56	Need help with comparator OAL I am preparing to reload for the first time in the 223 variety for 2 AR-15's (DPMS & Armalite). I checked both chambers using a Stoney Point OAL Gauge and bullet comparitor with Hornady 75g HPBT bullets. Now for my problem and confusion. I measured each rifle with the same 5 bullets. The DPMS measures 2.969+/-0.001, the Armalite measures 2.860 with 2 bullets and the remaining 3 bullets at 2.851, 2.855 and 2.856. These are actual vernier measurements with the comparitor attachment that is 1 inch long. My questions are: 1) Is throat variation from brand to brand as large as 0.1 that I measured? It seems like the DPMS has a very long throat. 2) Why does the Armalite give 2 sets of measurement groups? 3) If I set the length at 0.020 from the lands the OAL will be to long for the DPMS. Do I settle for the longest length that will fit the mag? The DPMS has about 1000 rounds and Armalite about 400 rounds through each. Thanks in advance for the help. Ray

July 3, 2002, 08:18 PM	#2
444 Senior Member Join Date: November 20, 2000 Location: Ohio Posts: 3,968	Ray, I can't answer your questions, but I would like to chime in here and say that I would also like some advice on using the Stoney Point tool. I can't get consistent measurements either. I am sure it is because there is something I am doing wrong; obviously the chamber isn't changing dimensions between readings. I have tried using a different bullet each time in case I deformed the bullet in some way etc, yet no two readings are the same. Help !!!! Two guys looking for answers. __________________ You know the rest. In the books you have read How the British Regulars fired and fled, How the farmers gave them ball for ball, From behind each fence and farmyard wall, Chasing the redcoats down the lane, Then crossing the fields to emerge again Under the trees at the turn of the road, And only pausing to fire and load.

July 6, 2002, 10:05 AM	#6
rick_reno Junior member Join Date: May 28, 2002 Location: Idaho Posts: 917	Need help with comparator OAL I've had the same problem you're havng with this thing. For me it works the way I think it's supposed to work on some guns, on others I also get different measurements regardless of how many times I attempt to measure it. I shoot a lot of Sako rifles and this tool works great on a 30-06, but I've got a heavy barreled 308 that I've never been able to get the same measurement twice on. A suggestion that might help you is to tap (use a small plastic hammer) on the sliding piece until the bullet sticks in the lands, set the screw and push the bullet out from the muzzle with a cleaning rod. I don't know if that'll help with the end result you're trying to obtain, but it should give you consistent numbers.

July 5, 2002, 01:09 PM	#3
Dave P Senior Member Join Date: August 16, 1999 Location: North Florida Posts: 1,346	1) Is throat variation from brand to brand as large as 0.1 that I measured? It seems like the DPMS has a very long throat. Yes every rifle is different; there is no standard for the throat that I know. If you have a stock rem 700, the bullets normally cannot touch the lands, they are out there so far! 2) Why does the Armalite give 2 sets of measurement groups? Beats me, but that repeatability (+/- 5 mil) is about what I see with a smoked bullet/split case method. I need someone to prove to me that they can accurately measure seating depth (repeatably) to a couple of mil! I say, don't sweat it! 3) If I set the length at 0.020 from the lands the OAL will be to long for the DPMS. Do I settle for the longest length that will fit the mag? If you are loading for accuracy, load for each rifle individually, and don't use a magazine.

July 6, 2002, 12:14 AM	#4
NoSweat Member Join Date: July 23, 2001 Location: Missouri Posts: 16	I had some problems measuring with the Stoney Point when I first tried it. The secret is to TAP the rod to push the bullet firmly into the rifling. If you push it in gently, you will get erratic readings. A good firm tap ( done consistantly) on the rod before tightening the thumbscrew will give consistant readings on your caliper. I have also used the RCBS Precision Mic. It will give consistent readings but the number differs from that on the Stoney point. I have stayed with the Stony point as it is easier to use. I check every 5 or 10 rounds to see if the seating is changing. It WILL CHANGE if you use a different lot of bullets.

July 6, 2002, 06:37 AM	#5
444 Senior Member Join Date: November 20, 2000 Location: Ohio Posts: 3,968	This may sound silly, but what do you mean specifically by "tapping". When I was doing this, I took my index finger and tapped on the end of the rod. I tried to use the same amount of force and tap it the same amount of times. I really went out of my way to be consistent in every aspect but obviously, I was not consistent enough. If you were getting good, consistent readings, please describe in detail, your method.

July 6, 2002, 03:44 PM	#7
NoSweat Member Join Date: July 23, 2001 Location: Missouri Posts: 16	444.... I forgot to mention one thing. Don't let the bullet in the case touch the rifling before you tap it into place. I won't call it "slamming" the bullet into the rifling, but a tiny slam, or a tap to send it home is what I use. Yes I use my finger for this. I got this technique from a buddy who said he got it from Sierra. The actual measurement is really not that important. You still have to load a series of Overall Lengths, and test fire them to find the best OAL for your rifle. I recently did this with a Hart barreled Rem 700 in 22-250, and was using a Sierra # 1410 52gr HPBT. I found the most accurate position was about .010 off the lands. I then tried some Sierra # 1400 53gr HPFB, and it also shot the best at .010 off the lands.