Vertical stringing

[chino69]

I'm looking for some advice because I know I've read an explanation for this before. I'm working up a live varmint load for the ferocious Pennsylvania groundhog. The load consists of Varget, Wolf small rifle mag. primers and Hornady's 87grn. V-Max. I shot this load the other night with calm conditions, no mirage; excellent conditions. The range was 200 meters, Rem. trued 40X single shot, sleeved bolt, etc., Kreiger 1:7.5" 6mm BR light varmint barrel. This rig is solid, having shot many heavier loads very accurately. There is nothing mechanical or optically deficient in the set-up. So here's my question: As I was working up the loads my groups were stringing verically upward. Any ideas out there? My first instinct is to try a Federal small rifle primer but I seem to remember the cause for vertical stringing to be something other than primers.

Any help would be appreciated.

Lou Baccino

 

[Old Gunner]

I've seen an article by a competition shooter that stated that he began having verticle stringing when using Varget.
He found that there was an area of carbon build up in the bore, when he cleaned it throughly the stringing disappeared.

Carbon build up can effectively reduce bore size by a thousandth or more in a localized spot, this allows a certain amount of blowby just beyond this constricted area.

You seldom hear of it being noticable unless thousands of rounds are fired, but the pattern or verticle stringing is a tell.

Other factors may be at work since carbon also increases copper fouling and can layer with copper fouling making each harder to remove.

If its not from carbon that would leave bedding and barrel heating as the next possiblity.

 

[abintx]

Lou ...

Here's Speed Gonzalez's treatise on curing vertical stringing: http://www.6mmbr.com/verticaltips.html. And, don't forget all the information Gene Beggs has provided in this site on eliminating vertical via the use of powder charges and/or a tuner. Art

 

[chino69]

Thanx for all the replies. Carbon build-up is not a problem as I incorporate a borescope into my cleaning regimen. I thought about the powder being too slow but was hesitant to go there because a healthy dose of Varget in my 1:14" twist Hart puts 65 grn. Hornady V-Maxes into a nice tight cluster @200 meters. I read Speedy's article and that was the one I was looking for; I knew I had seen it before.

Again, thanx for the replies.

Lou Baccino

 

[D R Greysun]

Thanx for all the replies. Carbon build-up is not a problem as I incorporate a borescope into my cleaning regimen. I thought about the powder being too slow but was hesitant to go there because a healthy dose of Varget in my 1:14" twist Hart puts 65 grn. Hornady V-Maxes into a nice tight cluster @200 meters. I read Speedy's article and that was the one I was looking for; I knew I had seen it before.

Again, thanx for the replies.

Lou Baccino

Lou,
There may lay your answer, 7.5 is a bit tight even for 87 grains V-Max.
D R

 

[chino69]

Too tight?

Lou,
There may lay your answer, 7.5 is a bit tight even for 87 grains V-Max.
D R

Do you mean too fast a twist? The point I was trying to make is that I have another barrel with a 14" twist that shoots one hole groups with 65 grn. V-Maxes and 34.5 grn. Varget. One of the above posters suggested that Varget may be a little slow and I used the 14" twist barrel shooting Varget as a counter argument. Am I missing something?

Lou Baccino

 

[D R Greysun]

Do you mean too fast a twist? The point I was trying to make is that I have another barrel with a 14" twist that shoots one hole groups with 65 grn. V-Maxes and 34.5 grn. Varget. One of the above posters suggested that Varget may be a little slow and I used the 14" twist barrel shooting Varget as a counter argument. Am I missing something?

Lou Baccino

Lou,
Please no arguments, I would not disagree with Mr. Salazar, he has a magic touch when it comes to 6BR. Yes, I was suggesting the 7.5":1 turn is on the fast side for 87gr. V-Max. I have found 10:1 to more appropriate for the 87gr. V-Max. You may want to consider 107 to 115 gr. bullets for your 7.5:1 barrel. You may find those 'one hole' groups returning. Good shooting.

D R

 

[chino69]

Lou, I would suggest trying H4895, Varget is a little on the slow side for that bullet. Of course, if you don't have some on the shelf, any powder is tough to get right now... A bit more Varget, if you aren't already maxed is another approach.

German,
Thank you for the reply. A little more Varget just opened the groups. I'll try H4895 in the near future. Do you suppose 1:7.5" twist is too fast?

Lou Baccino

 

[chino69]

Lou,
Please no arguments, I would not disagree with Mr. Salazar, he has a magic touch when it comes to 6BR. Yes, I was suggesting the 7.5":1 turn is on the fast side for 87gr. V-Max. I have found 10:1 to more appropriate for the 87gr. V-Max. You may want to consider 107 to 115 gr. bullets for your 7.5:1 barrel. You may find those 'one hole' groups returning. Good shooting.

D R

DR,
Thank you for your reply. You may be right about the twist being too fast but I haven't given up yet. I'm waiting to hear other opinions.

Lou Baccino