Need help with understanding the COAL and OAL from the rifling for my .308.

[dlouie87]

Hello,

I recently purchased a Hornady OAL tool and was wondering if you folks can tell me if I'm doing this correctly. Before this tool, I was just loading 175 SMKs to 2.800 as most reloading books recommend. I've been researching the threads in this section about seating depth and I wanted to double check my process. Please correct me if my terminology is incorrect as I want to make sure I'm understanding this process.

I already bumped the shoulder back .002'' from the once fired brass but now I'm confused on determining OAL and COAL.

I took the average of 10 readings with a 175 smk and that reading was : 2.195'' from ogive. The longest was 2.207 and the shortest was 2.184. I understand that there can be variances between the bullets but I want to get within the ballpark.

I took that exact bullet and seated it to 2.800 COAL and the OAL from the ogive came out to 2.230''. Does that put that loaded cartridge at .035'' jammed into the lands/rifling? I pulled that bullet and re-seated it to 2.191 measured from the ogive and the COAL came out to 2.775''. Should I be concerned that the COAL is .225'' shorter than the reloading manual's recommendation?

I remember reading that it is recommended to start with the bullet .010'' jammed into the lands so would I want to measure 2.205 from the ogive and have the COAL be shorter than the reloading book's recommended 2.800'' COAL?

Just for a reference, the Federal Gold Medal Match 175gr has a ogive OAL measurement of 2.225. In a safe area, I chambered the Fgmm and the ogive did not change. I thought maybe the rifling would shorten the FGMM's OAL to what I measured (2.195'') since it would jam the bullet in further. Am I doing something wrong or am I just not getting how this works.

Would you go with the 2.800 COAL and have the cartridge be jammed .03 into the lands or go with my recording of 2.195 OAL from ogive (touching the lands) and be a .025 short of the reloading manual's recommended COAL of 2.800?

Thanks you for reading and I hope that made sense.

DL


**Update #1**
7/13
I found out that the Bisley reamer that was used for my build is designed accept a shorter cartridge. So my COAL of 2.775 should be ok to shoot. I'll update this thread after I do the OCW at that COAL.

**Update #2**
7/14
So went and shot a OCW today with the COAL of 2.774. No pressure signs with the near max and max load.

Here are some pictures:





Here is how it shot 168smk FGMM (10 shots in the big target) and 175smk Southwest ammo (3-shots on the botton) without any pressure signs. These were 2.795 COAL and there were no problem with extracting a live rounds.




Overall, I think this Bisley Chamber is going to be great from the groups I've seen. I'm going to try to find a load and stretch it out to further distances to see how it performs.

DL

 

[buffybuster]

Are you using the Hornady supplied case to measure to the ogive? I'm asking because there should not be that much variance in your readings from 2.184" to 2.207"

What I do is take a fired (unsized) case, partial neck size the caseneck only, notch the neck if needed, to lightly hold a bullet (not loose but not too tight). Pull the bullet in the case so it's long, carefully slide it into the chamber and slowly close the bolt. Then slowly extract the cartridge. Measure the distance to ogive. Some recommend removing the plunger ejector, if your action has one, to remove any pressure on the case. I find using a fired case negates the plunger.

 

[No1]

You should know if your bullet from your previously loaded ammo is into the lands by chambering a loaded round, then ejecting and examine the ogive of the bullet for tell-tell marks that it has come in contact with the rifling. .030-.035" into the lands won't push the bullet into the case unless the neck tension is loose.
My opinion is that you are over-thinking this. Use the Hornady OAL tool to find where your bullet touches the rifling. You can choose to measure off of the ogive or the OAL of the cartridge, that's up to you.
There is nothing wrong with seating into the lands or off the lands or just shy. Your rifle will tell you what it likes.

 

[SeattleDude]

It sounds like you have Savage 10

Just measure the chamber few times. Consistent very light pressure on bullet. Good pressure on Case and make sure case doesnt move.

When you do it few times you will get more consistent readings. Then for your bullet seatting back off .010 and seat them .

I have same issue with 175gr SMK bullets in my Savage 10. Just have to seat them little shorter.

 

[dlouie87]

Buffy - I am using the hornady supplied case. I'm going to make the case using my once fired brass and use your method. I thought the difference between the longest measured and shortest measured was large too. Most of the measurements were consistent with the 2.195'' average.

No1 - I think I am over thinking it. I'm going to try the method mentioned above and see if I can get a better reading with less variance.

Seattledude - It's a Defiance Deviant. I'm going to try the measurements again tomorrow.

Thank you for your replies.

 

[Sweetyzfd]

Tag for later

 

[dlouie87]

Hey guys,

I found out that the Bisley reamer used for my rifle is meant to work with shorter cartridges. I measured the OAL of the ogive with 3 different methods and they all came back with .005'' of eachother so I know the throat is cut short. I'll perform the OCW with my COAL 1.775 and I'll report back. Thank you for all the help!

 

[haroldwilson]

I think a Bisley reamer has .080 throat length. It is set up for 155 gr bullets for Palma. Why did you get a barrel chambered with that reamer?

If this is what you have, you might think about having the chamber throated out longer for shooting 175-200 gr bullets. Shooting the larger bullets seated short can lead to issues like having the boattail below the shoulder neck junction. This is not optimal.

 

[dlouie87]

I didn't really think about it. I trusted my rifle builder and I just supplied him with my old stock, then asked him to build me a .308. I don't have any regrets. I shot 10 shots to break it in a few days ago and it shot great. I didn't post a picture because it took me seven shots to get my zero dialed in and only had a 3 shot group shot. That was with factory ammo so when I was trying to reload earlier today, I ran into the problem of not knowing my rifle was chambered with a bisley. Now that I know about the chamber and after I talked to him on the phone, I'm going to try the loads I'm going to load this week. I hope to get the 175s to 2650-2700 fps and to find the accuracy node by doing the OCW test. If I'm unsatisfied, I'm confident that my rifle builder would do his best to make it right.

 

[haroldwilson]

How long is your barrel?

 

[dlouie87]

24''. More realistically it'll be 2600-2650. 2700 would be a pretty hot load.

I have found some threads through google and seems like there are mixed reviews but the people with the barrels and the bisley says that shooting the 175s would shoot just fine. I know every rifle is different so I'm going to try to find a load this this one.

Also found this about the bisley:
http://www.snipershide.com/shooting/sniper-hide-gunsmithing/147070-308-reamer.html

The freebore on the reamer used is the newer model with .088 FB instead of the .080

 

[dlouie87]

Updated with new info. I think the Bisley chamber is going to be fine.

 

[gstaylorg]

The Bisley reamer is very similar to the standard PTG reamer GAP uses on the majority of their .308 rifles (.324 nk. 1deg30, .085" fb). I have several GAPs with this chambering and have no trouble loading anything up to the Berger 185 Juggernaut (.020" jump). Obviously, the 185s aren't loaded to mag length, but you get the idea. The Bisley chamber with .088 fb should work just fine for anything up to the 185 gr range, with 175 gr bullets and less easily loading to mag length.

FWIW - I shot the Applied Ballistics 175 Tactical load out of these rifles for quite some time. Velocities ranged from ~2650 fps out of a Crusader (23" barrel) to ~2710 fps from a Hospitaller (24" barrel). This was not a "hot" load by any means. With hand loads, you should easily be able to get velocity in the 2700-2750 fps range out of a 24" barrel with no pressure issues at all.