Seating Depth in the 270 WSM

[DrMike]

I have taken it as a matter of faith that seating as close to the lands as possible increases accuracy. I read Steve Gash's article in the March issue of G&A, in which he loads 0.030 inches off the lands for all bullets save the TSX and the E-tip. I have only tried four sets of loads in my 270 WSM at that seating depth. I did not note a significant increase in accuracy, nor a degradation of accuracy. I intend to test this more extensively over the coming weeks, especially if the weather co-operates to permit me range time.

I have seated between 0.020 and 0.010 inches off the lands for previous work with the 270 WSM, and also for the 7mm WSM, the 300 WSM and the 325 WSM. All have given me superb accuracy within this range of seating depths.

I'm wondering if others who are shooting this particular calibre, or even the other WSMs or SAUMs, have made similar observations to those of Mr. Gash? Freebore is not necessarily detrimental to accuracy, as is evident from Weatherby's. However, it would be interesting to see what depths are being used by others on this board.[/quote]

 

[Richracer1]

I have the 130ET loaded up for my 270WSM with a COL of 2.88, which even closer to the lands than my 140AB (2.875"). I don't remember what measurement I got with the 140AB to touch the lands. I don't recall my group size, but here's my recipe for the 130ET and my 270WSM:
60.5gn of IMR4350
Win Brass trimmed to 2.09"
GM215M
COL: 2.88"

 

[DrMike]

RR,

What sort of velocities are you getting with that load. I have some 130 E-tips. I haven't loaded them yet, though they are on my list to load this next week. I was planning to work up to 72.5 grains of Magnum. Simultaneously, I'll likely work with seating depth and 130 grain TSXs and H100V. This gave me good group (0.37 inches) and velocity (3114 +/- 9) at 0.030 inches off the lands. It was the best group of six loads tested in my current 270 WSM. I have focused on 130 grain bullets so far, but I am also working up some loads with 140 grain A-frames next week.

 

[Teknys]

I shoot a Sako75 in a 270WSM. With the box mag I can only load to that max length and with the 150 part I'm about 85 - 90 out. I wish I could cut that in half. With the 130 Scirocco I was about 120 out. Groups and pressures were good. With the 130gn I was at 3210fps. With the 150 I'm around 2900. I'm going to push until I see signs with the 150 PT this spring. I too have a supply of the 140gn Accu and am going to work that up this spring and use it on Whitetail this year. Again I'm stuck with the small (short) box magazine in the Sako.

 

[Richracer1]

Sorry, I haven't chrono'd this round, yet.

I too have a blind mag, but 2.88 has no problems fitting, but my WSM is a Win Mod 70 Super Shadow. This was the first rifle I ever bought. It was one of those Wal-mart special Winchester package deals.

 

[DrMike]

I'm shooting one of the new Winchester Featherweights, and there is ample room in the magazine to permit loading out to the lands. I intend to try the load you worked up in addition to the others I mentioned earlier. I do want to play with seating depth, however, as that is just intriguing.

 

[blacktailhunter]

My favorite 270WSM load is one from Layne Simpson. I have shot this load ever since I could get a hold of Magpro. It is over book in the new Nosler manual, but as we all know, using custom pressure test barrels will yield different results than a factory chambered barrel. Please work up carefully from MINIMUM CHARGE. I own several short mags and have friends with several short mags, and none of them have the same max powder charge.

My load is:
Remington Cases
72.5gr Magpro
WLRM primer
140grn Nosler AccuBond
3260fps ave @ 75* F
I don't have my COL, but I do know that it is .088" off the lands.

 

[DrMike]

Don't know about Simpson's load, but Lane Pearce loaded up to 74 grains of MagPro behind a 140 AB. I've shot that load, but groups were not as good as the rifle was capable of. What is intriguing to me is that you have quite a jump to the lands. I'll definitely be working on this.

 

[russ808]

For my 300wsm out of a vanguard:
imr4350@63.5 grains
CCI-250
oal:2.870
180 partitions
Sorry don't have a chrono. so I can't give you the FPS

for the 180 AB's
everything is the same except for 64 grains of imr4350

 

[Alaska]

http://www.realguns.com/archives/078.htm

65.0 of RL 22 with 130gr TSX
Fed 215M
2.80" COL

 

[blacktailhunter]

DrMike, I am familiar with the 74.0gr load. That has been the standard maximum charge for Magpro and a 140grn bullet. My rifle started sticking the bolt at 74.0, so I worked back up from 70.0 grains. This was after several lengthy range sessions with loads starting at 66.0 grains. After analyzing chrono and group data, I determined that the maximum charge in my gun was was 73.3gr. I settled on my load of 72.5 due to the very low extreme spread and delightful standard deviation. My COL is actually started with the longest that I was comfortable having in the magazine of my Remington 700 SPS. This was a special run that was not cataloged by Remington. From that length, I seated groups of loads in .005" increments and documented the results. I found the "valley" at .088" off the lands. I tested this again with loads .090" off and at .086" off to confirm. This rifle likes this powder charge at this seating depth the best.

A few things to note while determining the distance to the lands in your rifle. While there are several way to do this, I use the Stoney Point/Hornady tool.
1. measure the distance on a clean barrel and put it in your load records.
2. measure it again when your barrel is slightly fouled. record it.
3. measure it again when the barrel is broken in if it is a new rifle. Record it both clean and fouled.
4. Once you determine if you rifle shoots better with a clean barrel or a fouled barrel, measure that distance and use it for your permanent load data. My rifles do not shoot as well on clean barrels and there is a slight difference in the distance to the lands when the barrel is clean compared to slightly fouled. This is not so critical with most short mag rifles since it is difficult to get real close to the lands. My .280 is a different story. If you are one of those who likes the bullet .001-.002" off, the difference between a clean or dirty barrel could very well put the bullet into the lands.

Sorry for the lengthy post and slight hi-jack, but I just like to share what I have learned with many hours of work with several short mags.

 

[DrMike]

Blacktailhunter,

Thanks for the post. I appreciate the care you have taken to determine your data. It looks good. Actually, I have never considered measuring the difference between a fouled barrel and a clean barrel. I have always measured on a clean barrel. To this point, all my rifles have shot to the same POI from a clean barrel. For the first time, on this 270 WSM, I'm noting a different POI from a clean barrel. It is one of the new Model 70s. So, I'll check this information as you have suggested. My previous 270 WSM had the same POI from either a clean or a fouled barrel, so I had not considered this.

For most of my rifles, I have discovered that for most bullets, a seating depth of from 0.010 to 0.020 inches off the lands gave me the best groups.

I do use the Stoney Point OAL gauge. However, I will check the OAL from a fouled barrel as soon as I am able to get back to the range. Our temperature dropped again, and it looks like a series of -23 to -28 days this week. I think I'll stay in.

Again, thanks for your informative post. There is quite a bit there to chew over.