Factory cartridge base-ogive vs modified case/bullet shoved to lands

[trdjohn]

Factory Hornday 6mm ARC Black (105 gr BTHP) cartridge base-to-ogive is measuring 40 thou longer, than base-to-ogive using my Hornady 6mm ARC modified case & 105 gr BTHP bullet pushed hard against the lands.

The factory black ammo OAL measures 2.200" +/- .002; using the modified case & bullet shoved into lands my OAL is ~ 1.965".

If I cycle a factory cartridge, the bolt closes (this is AR platform), and then measuring the factory rounds after chambering shows no change in cartridge base-to-ogive or OAL. I would think the factory cartridge would shorten up?

Measuring the factory round and modified case headspace dimension, they're the same.

Why can I only push my bullet 40 thou less than factory cartridge base-to-ogive? Why/how is the factory ammo closing on the bolt?

confused...

 

[Zero333]

I've had the same issue with FGMM 168 smk. The factory ammo was loaded around 2.800" and when I used the AOL tool (but with the reloading component 168smk) it touched the lands at 2.750"... I should of taken out the factory bullet out of the factory ammo and checked with the same exact bullet. But I didn't feel like it.

However... with the same barrel I can load 2.775" with 168 smk and the bullet is not jamming even tho the Hornady OAL tool using the same bullet shows 2.750" as touching.
I think it might be just tight freebore.

 

[Coyotefurharvester]

Could be an alignment issue, using the Hornady tool you are able to put a slight angle on the case body and the resulting angle on the bullet making feel like you are "tight" in the lands. WAG that can be checked.

 

[MrK.]

I have actually had the same issue with my CMMG 6mm ARC. Hornady black just seems to kiss the lands but extract easily. I load 95 SSTs to the same ogive length and I need to mortar the gun to extract them, sometimes pulling the bullet in the process and making a mess. I had to seat a couple thousands deeper for reliability. Weird

 

[memilanuk]

Are you using the curved model or the straight model of the Hornady tool?

'Hard against the lands' with the one is not nearly the same as with the other, in my experience.

 

[trdjohn]

Thanks for the replies and thoughts. I'm using the straight Hornady tool, I have the curved one, but the curved one uses that flexible cable to push, and don't think I'd get as much oomph pushing the bullet. But I may try it anyway....

It could be the case is going in at slight angle, I've had that before, and wound up using a wooden dowel to help guide the bullet into the lands better. I did that here too, but didn't see a change.

When I cycle a factory load in and pull it out, there is more scratching along the bullet jacket toward the nose, more so than if I use the modified case and bullet, so it might be tight freebore like suggested.

I've only shot about 15 rounds of factory and they didn't group as well as other factory hornady ammo. I might try some at the cartridge base-to-ogive length my comparator shows, see how that goes.

john

 

[divingin]

Factory Hornday 6mm ARC Black (105 gr BTHP) cartridge base-to-ogive is measuring 40 thou longer, than base-to-ogive using my Hornady 6mm ARC modified case & 105 gr BTHP bullet pushed hard against the lands.

If I cycle a factory cartridge, the bolt closes (this is AR platform), and then measuring the factory rounds after chambering shows no change in cartridge base-to-ogive or OAL. I would think the factory cartridge would shorten up?

If you cycle a factory cartridge and extract it, does it show any rifling engraving on the bullet? If not, you're not hitting the lands, and it won't shove the bullet into the case. If you do the same with one of your loads, do you get rifling marks?

I suspect the problem you're having is due to taking the tool results as reality, when they may not be.

If you take an unprimed (for safety) case, barely seat a bullet, and force the chamber closed (case lube on the ogive and/or using a rod to start extraction may be needed if the bullet is firmly into the rifling), what does that CBTO measure? That should give you decent rifling marks, and an idea of where the ogive is when it's actually engaging the rifling (it should be a hard jam measurement, and you may need to shorten up by .010 to .015 to get to the touch point.)

 

[Zero333]

Are you using the curved model or the straight model of the Hornady tool?

'Hard against the lands' with the one is not nearly the same as with the other, in my experience.

I use the curved Hornady OAL tool, and the results are within 1 or 2 thou compared to the @Alex Wheeler method. I do however use the OAL tool with the rifle barrel pointing upwards so it aligns straight with the chamber and freebore.

 

[memilanuk]

I use the curved Hornady OAL tool, and the results are within 1 or 2 thou compared to the Wheeler method.

Interesting. A number of years ago we were trying to find a way to compare load data between team guns with what *should* have been near-identical chambers. Problem was what shooter (loader) A considered 'touch' and what shooter 'M' considered touch varied considerably. A lot of people were using the curved Hornady tool and found they were 10-20 thou off compared to the Wheeler method. I had been using the straight version (mine was old enough it still said 'Stoney Point' on it) in a pretty heavy-handed manner (relatively speaking). My numbers were within a thou of what I got with the Wheeler method. At the time, the decision was made for *everyone* to use the Wheeler method so the shared data made a little more sense.

 

[Zero333]

Interesting. A number of years ago we were trying to find a way to compare load data between team guns with what *should* have been near-identical chambers. Problem was what shooter (loader) A considered 'touch' and what shooter 'M' considered touch varied considerably. A lot of people were using the curved Hornady tool and found they were 10-20 thou off compared to the Wheeler method. I had been using the straight version (mine was old enough it still said 'Stoney Point' on it) in a pretty heavy-handed manner (relatively speaking). My numbers were within a thou of what I got with the Wheeler method. At the time, the decision was made for *everyone* to use the Wheeler method so the shared data made a little more sense.

Indeed it's all about feel and knowing the difference between touching the lands and jammed in the lands.
Difference between touch and jam can be quite a bit depending on bullet and chamber.

 

[trdjohn]

If you cycle a factory cartridge and extract it, does it show any rifling engraving on the bullet? If not, you're not hitting the lands, and it won't shove the bullet into the case. If you do the same with one of your loads, do you get rifling marks?

Yes the factory ammo has marks down the bullet...I had mentioned it in the post above yours. "When I cycle a factory load in and pull it out, there is more scratching along the bullet jacket toward the nose, more so than if I use the modified case and bullet....."

The pic of just a bullet is from using the hornady tool and one of my bullets, it shows some scraping. The other picture is factory ammo, I've circled in blue how much the bullet gets scraped, this is from placing the bullet into the chamber by hand and the bolt closed, so it's not the feed ramp, scraping it up.

I suspect the problem you're having is due to taking the tool results as reality, when they may not be.

When using the tool, I can't push any harder on the bullet to get it any deeper, that's the reality.

If you take an unprimed (for safety) case, barely seat a bullet, and force the chamber closed (case lube on the ogive and/or using a rod to start extraction may be needed if the bullet is firmly into the rifling), what does that CBTO measure? That should give you decent rifling marks, and an idea of where the ogive is when it's actually engaging the rifling (it should be a hard jam measurement, and you may need to shorten up by .010 to .015 to get to the touch point.)

 

[Coyotefurharvester]

The blue circled scrape, ramp/barrel extension or magazine contact. Second pic, bullet that you made (pushed) contact with throat/lead (that isn't concentric). Make up a few dummy rds, starting at Your length(Hornady tool) and every + 0.010 to factory length + 2 more. Chamber and extract. Find the max length where dummy will chamber and extract properly. This is where a bullet ogive COMPARATOR comes in handy, as you can compare before and after chambering lengths to the factory production rds.

 

[trdjohn]

So I just monkeyed around with the 105 gr BTHP again, using @Zero333 idea of holding the receiver vertical while pushing the bullet in with the modified case and tool, that did the trick! I was able to push the bullet much further out from doing it horizontally, it was actually a thousandth or two beyond where the factory ammo base to ogive is.

Must be that tanget ogive of the BTHP hanging up some where. That factory ammo must be really close to the lands.

My 103 ELD-X and 108 ELD-M bullets didn't seem to matter using the tool horizontal or vertical to find the lands, both measurements were the same.

Thanks for the suggestions.

 

[Zero333]

So I just monkeyed around with the 105 gr BTHP again, using @Zero333 idea of holding the receiver vertical while pushing the bullet in with the modified case and tool, that did the trick! I was able to push the bullet much further out from doing it horizontally, it was actually a thousandth or two beyond where the factory ammo base to ogive is.

Must be that tanget ogive of the BTHP hanging up some where. That factory ammo must be really close to the lands.

My 103 ELD-X and 108 ELD-M bullets didn't seem to matter using the tool horizontal or vertical to find the lands, both measurements were the same.

Thanks for the suggestions.

100 % for sure the 105 bthp has a tangent ogive.

I've been using those bullets ever since they came out.

I remember they were cheaper than the 105 A-max. I still have a few hundred 105 A-max.
I could not get the newer 108 ELD-M to shoot as good as the A-max or the bthp.
107 smk are still my favorite because they shoot as good as the 105 Berger VLD & Hybrid but don't cost as much.

 

[William Vogel]

Has anyone measured the headspace of the modified case to compare it to your brass. The Hornady modified case only measures from the shoulder to the lands realistically. I have several and use them in my 308’s 6.5’s and 223’s and I have good success with them but I don’t use any factory ammunition in my rifles.

 

[Zero333]

Has anyone measured the headspace of the modified case to compare it to your brass. The Hornady modified case only measures from the shoulder to the lands realistically. I have several and use them in my 308’s 6.5’s and 223’s and I have good success with them but I don’t use any factory ammunition in my rifles.

All I can say is the OAL modified brass measures the same ( from head base to Datum line ) as the Go-Gauge of the same cartridge.

Your chamber could have anywhere from 0.002" to 0.0035" of H-S.
Military cartridges like 5.56 Nato and 7.62x51 have different H-S measurements than their 223rem and 308win brothers.

So if you bump the shoulder 0.002" of a fully fire-formed piece of brass, the sized brass should measure anywhere from 0.0015" to 0.0025" longer (base to datum) than the modified brass.

 

[JB10]

I had same issue with a ruger american in 6mm creedmoor. Factory 108 eldm was .020 longer than what i could measure. I was even sticking the bullet in the rifling to where i had to give it a push it out with a cleaning rod. But when loading a factory round in and removing it there were no marks on the bullet form even touching the rifling

 

[JEFFPPC]

What you measure vs what someone else measures is of no importance . What is important is that your method is repeatable. Now you have a reference point. All that is necessary.