Help on ogive measurement

[paigecm]

Ok. I have never had this result before and want to see if anyone else has and what your thoughts are on it. I just recently horse traded my way into a GAP 308. I wanted to start working on loads so I used my hornady oal gauge to get a reading. I am coming up with 2.146 on a 175 gr Nosler hpbt after mic is reset to zero with bushing in. That puts the coal at 2.745 well below all recommended starts of 2.80. I have never had a rifle show less than the saami spec.
Now I have only used this type of measurement process on 3 rifles before but they have all been longer than they”start”length. So from here do I load at say 2.765? Sure does look short to me? And what powder charge?
At 2.8 I can see on the bullet where it is contacting the lands.

 

[isofahunter]

3 in a martini, dirty.

 

[straightshooter1]

Ok. I have never had this result before and want to see if anyone else has and what your thoughts are on it. I just recently horse traded my way into a GAP 308. I wanted to start working on loads so I used my hornady oal gauge to get a reading. I am coming up with 2.146 on a 175 gr Nosler hpbt after mic is reset to zero with bushing in. That puts the coal at 2.745 well below all recommended starts of 2.80. I have never had a rifle show less than the saami spec.
Now I have only used this type of measurement process on 3 rifles before but they have all been longer than they”start”length. So from here do I load at say 2.765? Sure does look short to me? And what powder charge?
At 2.8 I can see on the bullet where it is contacting the lands.

That 2.146 just doesn't sound right for a bases to ogive measurement on a 175 gr Nosler. Not sure what you mean by "with bushing in" and how a mic might be used??? You're not using a comparator gage on a caliper make the measurement, as typically done?

While it's not particularly unusual to have a bullet seated a little less than the 2.800 OAL in some cases, 2.745 is REALLY short. And if that chamber is really that short, maybe it simply isn't designed for the longer heavier bullets???

 

[paigecm]

I am using the comparator with the correct bushing. I just was stating that with that in the micrometer and it set to zero that was the reading I was getting.

 

[hafejd30]

If your contacting lands at 2.8” that seems like it’s very short. Did the previous owner change the barrel out or is it factory GAP?

Is this bolt or gas gun?

 

[straightshooter1]

I'm sure you guys know bullet shapes will produce different COAL's. Not being sarcastic or trying to insult anyone's intelligence. The Nosler CC's have a very traditional bullet shape, short nose, and low BC.

Of course your right and for the most part that's why I referenced to the COAL. Apparaently he's not using the Nosler CC's and from his description and the picture, he's using the 175 Nosler RDF #53170, which is a much longer than the CC's, and of course would have a very different BTO measurement.

 

[paigecm]

Guys. I apologize for not putting in the exact bullet. It is the CC Nosler. It is a bolt gun. Crusader with original barrel at about 720 rounds.
When seated at 2.800 I can see marks on the bullet (175gr Nosler custom competition) where it is touching the lands. I definitely understand bullet shapes dictate the coal when loading based on ogive.
However I still don’t think I should be hitting lands at 2.145-2.146 and really coal doesn’t matter at this point as long as I am over the specified 2.8. Which I am under. If I am wrong on this let me know.
I spoke to GAP and they are not sure. Spoke to a very nice guy who asked me to try taking some measurements with 175 smks and see if it is still getting the same result. Also suggested could be a carbon build up in the chamber. Perhaps the Nosler cc’s are different. To me they are the same style bullet. Otherwise he said for me to see if I can’t make it shoot with a shorter bullet if not they would take a look at it.
He did tell me it could be tricky to “feel” good he lands. That is when I told him when I load to 2.8 I see the markings.
I will go home see if the 175 rdf’s touch, check if 168 fggm’s touch and recheck for the fifth time my measurements and post back. Sorry if I didn’t give all the right info to start.

 

[straightshooter1]

Guys. I apologize for not putting in the exact bullet. It is the CC Nosler. It is a bolt gun. Crusader with original barrel at about 720 rounds.
When seated at 2.800 I can see marks on the bullet (175gr Nosler custom competition) where it is touching the lands. I definitely understand bullet shapes dictate the coal when loading based on ogive.
However I still don’t think I should be hitting lands at 2.145-2.146 and really coal doesn’t matter at this point as long as I am over the specified 2.8. Which I am under. If I am wrong on this let me know.
I spoke to GAP and they are not sure. Spoke to a very nice guy who asked me to try taking some measurements with 175 smks and see if it is still getting the same result. Also suggested could be a carbon build up in the chamber. Perhaps the Nosler cc’s are different. To me they are the same style bullet. Otherwise he said for me to see if I can’t make it shoot with a shorter bullet if not they would take a look at it.
He did tell me it could be tricky to “feel” good he lands. That is when I told him when I load to 2.8 I see the markings.
I will go home see if the 175 rdf’s touch, check if 168 fggm’s touch and recheck for the fifth time my measurements and post back. Sorry if I didn’t give all the right info to start.

In my gun the 175 Nosler CC's touched the lands at 2.272 (and my 175 SMK's were 2.630). With yours hiting the lands at 2.145, that's a .127 difference and huge. . . though my gun is factory dimensions and DOES have a relatively deep throat. It'd be interesting see if factory 175 SMK cartridges fit or if you had a go and no-go gauges to see how that barrel/chamber if fitted to the receiver. . .

really hard to know without the gun in hand. I'd take the gun to a gunsmith and have him check it out.