How much .005" seating depth can change patterns

[TackDriver284]

I had finished shooting all 35 rounds of the 140 Hybrids in the 6.5 Creed on the last few range trips since last year. I was shooting them on 10" steel from 700 to 850 yards. I did not shoot as much as I used to. I had 4 charges in addition to test that I made last year in the fall season, but never got to test them.
My actual load shoots very well out to 850 yards on steel ( haven't tried them out further than that yet ) and tested them before I made the other 4 test groups, its 42 grains H4350, 10X fired Nosler brass, BR-2, and 140 Hybrids. Ogive is 2.216" exact. I believe its about .090" off the lands to fit the magazine. If I seated closer to the lands, the OAL is so great that its not possible to fit the mag. On those four 3 round test groups, loads are as follows:
A. ) 42 grains and 2.221" ogive ( .005" over my actual load )
B.) 42 grains and 2.211" ogive ( .005 " under my actual load)
C.) 42.1 grains and 2.216" ogive ( ogive is exact as my actual load)
D.) 42.2 grains and 2.216" ogive (ogive is exact as my actual load)
I tested those 4 three round groups this morning, variable wind was left to right 5-8 mph. The first two loads the ogive was changed which was .005" over my actual load, and .005" under and my actual ogive is 2.216" , the 3rd was .1 grain more powder and same ogive, and a ragged hole, and the 4th group was .2 grains over / same ogive and still a ragged hole. This test shows that changing just the ogive slightly can make a difference.

 

[DrMike]

Yes, the difference can be dramatic. Excellent work.

 

[JD338]

Very good information Mark.
Thank you for your time and effort.
Good stuff.

JD338

 

[RL338]

The thought was the Hybrids were suppose to be more forgiving in seating depth. You show there is work to be done with 0.005”
Nice work

 

[SJB358]

Very nice. That’s great stuff.

 

[Vince]

Very informative.

Vince

 

[Wolfshead]

I had to read this a couple of times to understand it.
My comprehension is not good sometimes.
This shows pretty distinctly that seating can have an impact on groups.
Then you have some who would say not to bother….
That last group, 42.2 looks very nice!

 

[NYDAN]

Mark, that is a great illustration of the effects of seating depth changes. That is one heck of a load you have. Thanks for sharing.

 

[TackDriver284]

The velocity was an impressive 2790 fps average with 4 fps extreme spread on the 42.2 grain load recorded off the Xero.

 

[xphunter]

Mark is very dedicated to the craft.
Mark lives in the comp world.
Finding a load that is great (great accuracy and single digit extreme spread), and will stay in tune is vital for the LR game.
WTG!!!

 

[TackDriver284]

Mark is very dedicated to the craft.
Mark lives in the comp world.
Finding a load that is great (great accuracy and single digit extreme spread), and will stay in tune is vital for the LR game.
WTG!!!

Thanks Ernie, I'm a meticulous and anal person when it comes to reloading.

Just decapped all 100 pieces of 6.5 CM brass, wiped them down, cleaned the necks with the RCBS station, annealed all the brass, and annealing gives the brass an ugly blue color, so I spun them on a drill with a rag damped with Kroil, to make them purty again and back in the ammo box they went to full size bush at a later time. While I was inspecting each piece, noticed that I had written PP on three cases, it means Primer Pocket, and last time when I primed it, I felt those primer pockets on those three cases were a little loose, needed to be tossed soon. I looked at the head of those cases closer, and could barely read the brass brand on it, it says Nosler and all along I had thought they were Lapua as I wrote in the above post, lol. So I edited it to Nosler brass. It's the only rifle that uses Nosler brass, all my other rifles uses Lapua, and only the 300 WM uses Norma and those new turned Lapua brass that I had to neck turn a few months back because of clearance issues.
I'm getting my 6 Dasher tomorrow that replaced my 6 BR barrel and going to use Alpha brass, the gunsmith used an Alpha reamer, and the barrel is 7:8 twist, 31 inch 1.250" to 1.150" straight taper in a pillar bedded A5 McMillian tactical stock and finished up with some Marine Tex around the action and stock. He installed a Impact Precision custom action to replace the old Rem 700 action I had before. I already have three 500 round boxes of 105 Hybrids, a 500 round box of 105 Hornady Match, a 50 round box of 105 VLD and a 250 round box of 103 Vapor Trails so I'm set for a while but I'll start with Hybrids and see how they do soon. Going to call Short Action Customs tomorrow for a full size bushing die and a seater with two bushings or maybe a Redding Type S. I use Redding Type S for all my rifles and they darn work for me. I will need some other items like a modified case, a case holder and cutter for my Giraud to trim those fired brass. I wanted to kick myself for not ordering those materials last week prior to getting the 6 Dasher, oh well I would have to wait then.

 

[bdbrown66]

Interesting thread, Mark. I read it the other day when you posted, and then had an even more dramatic example myself today.

I'm also doing load development for this Franchi Momentum 6.5CM that I bought last fall. Several different powders and bullets in the 130gr range. In this particular case, it's the 129gr Hornady SST, 38.5gr Varget, Sig brass, and Fed 210M primers. When I did the initial test to find the best charge weight, I just loaded them at .020" off the lands. Now that I settled on 38.5gr, I ran another test on the seating depth. All of these loads are identical, except that I varied the seating depth from .010" to .030" off the lands, in .005" increments. I personally have never seen such a dramatic change, but it was quite evident.

Here are the groups, in order:











And yes, there are 3 shots in that last group.

I'm going to run another test, from .030" to .050" and see how that goes. But for hunting purposes, I'm more than happy with that last result.

Cheers,
Brian

 

[TackDriver284]

Interesting thread, Mark. I read it the other day when you posted, and then had an even more dramatic example myself today.

I'm also doing load development for this Franchi Momentum 6.5CM that I bought last fall. Several different powders and bullets in the 130gr range. In this particular case, it's the 129gr Hornady SST, 38.5gr Varget, Sig brass, and Fed 210M primers. When I did the initial test to find the best charge weight, I just loaded them at .020" off the lands. Now that I settled on 38.5gr, I ran another test on the seating depth. All of these loads are identical, except that I varied the seating depth from .010" to .030" off the lands, in .005" increments. I personally have never seen such a dramatic change, but it was quite evident.

Here are the groups, in order:

View attachment 25433

View attachment 25434

View attachment 25435

View attachment 25436

View attachment 25437

And yes, there are 3 shots in that last group.

I'm going to run another test, from .030" to .050" and see how that goes. But for hunting purposes, I'm more than happy with that last result.

Cheers,
Brian

Good stuff, you getting there. I can see the changes of patterns. May I ask what your velocity is?
I would redo the last load in case its not a human error. The last load seems good.
Have you some H4350 to try? It's the bees knees for the 6.5 CM, I love it.

 

[bdbrown66]

Good stuff, you getting there. I can see the changes of patterns. May I ask what your velocity is?
I would redo the last load in case its not a human error. The last load seems good.
Have you some H4350 to try? It's the bees knees for the 6.5 CM, I love it.

It's running right about 2780 fps. Note that it's right at the max load per the Nosler data (38.5), and just slightly above the Hornady data (38.2). Sierra data for their 130gr bullets runs from 37.6 to 38.8, depending on the bullet. So I figured that it was safe enough to ease up to 38.5; I have not observed any pressure signs at that load. No extractor marks, sticky bolt, etc. ES and SD numbers are good, single digit SD over 15 shots. The last shot was a bit higher than the rest, which pushed the SD from about 7.5 up to about 9, but still pretty good. Varget is too fast for the 140+ bullets, but for 120-130gr, it's a solid choice.

I do have H4350, and I'm testing that with another bullet. The velocity point where I ended up with that load is about the same, right around 2780.

I will shoot that last group again, as my next test will go from .030-.050" off the lands. We'll see how it goes.

Brian