Last years load NOT making major!

[TwoShot]

I bought an STI Trubor in the spring of 2008. When I first got the gun I worked up a load with 7.3 gr Silhouette and an MG 124 gr.CMJ. The load barely made major at 166pf. I loaded up 500 rounds and started practicing with my new toy. I re-chrono'ed the load before loading any more and after nearly 500 rounds the average velocity dropped from 1340fps to 1280fps. I bumped the charge up to 7.5 and loaded 1000 more, same story, at the end of the 1000 I wasn't making major any more. I bumped the load to 7.75 and things seemed to stabilize. I shot that load all last year, chrono'ed it in August 2009 before I went to the Illinois Sectional, it made major but no cushion so I loaded ammo at 7.9 grains. This ammo made 1380fps/171pf at home and 170pf at the match. The gun now has 12,000 rounds through it. I chrono'ed my 7.75 load this spring and the average velocity was 1285/159pf. I had some of the Illinois Sectional match ammo left from last year, it chrono'ed 1338/166pf. The primers look like a 166pf load, not the 171pf they were last year. Is this normal? Do I just keep bumping the load up to make major? I am concerned as I read on the forums most people shooting Silhouette and MG 124's are in the 7.5-7.8 range. Thanks in advance for your help!

[Sarge]

Is silhouette temp sensitive? If it is you will have to chrono your loads in the same weather conitions every time in order to get consistency. I have used Tite group and solo1000 in 9 minor and found some pretty dramatic velocity swings between hot and cold days.

[TwoShot]

Silhouette is supposed to be reverse temperature sensitive. The loads from last August chrono'ed slower today and honestly the temp was similar.

[WDB]

Someone else had the same problem on here. Here's the read: http://www.brianenos.com/forums/index.php?showtopic=103907&hl=356&st=0

Good luck figuring it out

[RH45]

Did you change to a different lot number of powder, or primers?

I've seen lot numbers of powders change--a lot!

[TwoShot]

I did change to a different lot of powder and I thought that might be the issue. That is why I tested a know lot of ammo, the Match ammo left over from last year. Same bullet, powder, primer and oal is suddenly 50 fps slower. Thank you for the suggestions, For now unless I figure something else out I'm going to bump the load up and watch the cases and primers. I'm not trying to argue with anyone, I appreciate your suggestions, just thinking out load.

[BritinUSA]

The chamber of the barrel will expand over time and this expansion will rob you of some fps, though I would not expect this much depreciation. One option you may have is to get the chamber measured up and check that it is still within reasonable specs. A gunsmith should be able to help with this.

[Sudden Death]

Jim,

I have some HS-6 left over from my open gun you can have it , I think you might like it better.

[mda]

What about the Chrono?? Are you using a chrono in a box with IR light source? If not this ccan be a major source of inconsistant reading as natural light changes.

MDA

[G-ManBart]

The chamber of the barrel will expand over time and this expansion will rob you of some fps, though I would not expect this much depreciation. One option you may have is to get the chamber measured up and check that it is still within reasonable specs. A gunsmith should be able to help with this.

Who told you that? Were they saying longer, or larger diameter? LMAO....yeah, it might change by one ten thousandth every 50K or so. Throat erosion robs velocity, not chambers growing larger, and the case will seal to it just the same. Fluted chambers, that allow significant amounts of gas to pass the case don't even lose any significant velocity, and that's way more dramatic than chamber wear would ever be.

Edited May 28, 2010 by G-ManBart

[G-ManBart]

Chrono two days in a row, with slightly different lighting and you can get 50fps difference with the same lot of ammo loaded sequentially. R,

[lcs]

I have used Sil for years in many different open guns. Sil is definitely temperture sensitive. Cold weather and the PF goes up and the hotter it is the lower your PF. In the same barrel I am talking 171 PF in 75 degree weather and 165 in 95 or hotter weather.

I also have a used STI Trubor. My experience with STI barrels has me convinced STI barrels require higher amounts of powder to get the same PF as KKM, Sch, or Nowlin (I've had all of em). My experience holds true for 40, 9, or 38.

I would ask a friend to chrono your load in another open to see if there is a major difference or chrono someone elses known load to see how their load chronos in your gun and see what happens.

[TwoShot]

I have not had the opportunity to try my loads in another gun, will do that later in the month. I checked my chrono with some known loads through another gun and the results match my reloading records. I have thought about the issues with different lots of powder and or primers affect the ammo I loaded in 2010. I still come back to the chrono results from the match ammo loaded last year. It is chrono'ing 50-70 fps slower now than it did in August 2009. The temps now are slightly cooler than last summer, we are in a hot spell for the month of May. Using the match ammo loaded last year, I have chronoed it on three occasions in the last week or so with the same results. The only thing different is the additional wear on the barrel. Given the history of this barrel needing additional powder to make major, I don't know what else it could be. Suggestions and constructive criticism of my procedures and analysis are welcome!

[CCL]

I have not had the opportunity to try my loads in another gun, will do that later in the month. I checked my chrono with some known loads through another gun and the results match my reloading records. I have thought about the issues with different lots of powder and or primers affect the ammo I loaded in 2010. I still come back to the chrono results from the match ammo loaded last year. It is chrono'ing 50-70 fps slower now than it did in August 2009. The temps now are slightly cooler than last summer, we are in a hot spell for the month of May. Using the match ammo loaded last year, I have chronoed it on three occasions in the last week or so with the same results. The only thing different is the additional wear on the barrel. Given the history of this barrel needing additional powder to make major, I don't know what else it could be. Suggestions and constructive criticism of my procedures and analysis are welcome!

Jim, I've got a trubor barrel an comp also with about 23k on it and it seems to get slower as it ages. I run 8.3 of Sil with 121 grn MG at 1415 in 70 degree temps. So I'm not surprised.

By the way, slide cracked again....fatal this time!

Chris

[CocoBolo]

I'm guessing 9 major since you are not using enough powder for a 38 Super Gun. In my case the gun got to the point where I was getting concerned about pressure, and the charge was high enough to make the gun a little violent, and having a major in front of me I just went to the backup gun which makes 172/175 easily (38 Super), I also had 10K of .355 bulltes to shoot up. My 9 major shorty makes 172pf with 7.7gr of Silhouette but it is a Clark Barrel 4.25". You can pickup some velocity by chaging bullets to .356 this will give a better seal, and use small rifle primers for another 10 fps. Being a TruBore a little more gas will probably help it some. I just started using Silhouette so I don't know how much it varies by lot, and I don't know that you year old ammo was stored properly, and as g-man recommends crono several times.

These barrels do wear out, and they seem to vary some, but 50K and you can't find the lands in them. My backup gun has an STI barrel and I have no idea how many rounds it has eaten but it is a good one, makes power and groups well. Shoot some groups and see how it is grouping if its lost its accuracy then maybe its time for a new on.

Edited May 31, 2010 by CocoBolo

[TwoShot]

Chris, Sorry to hear about the cracked slide. I remember when we started shooting together, I thought you were using 8.0 grains of Silhouette. Now at 8.3, we are about in the same boat. Coco Bolo since you brought it up, my year old ammo was stored in a military ammo can, in a room with a dehumidifier maintained at 40% humidity and temperature between 70 and 78 degrees. NO offense taken to your bringing it up, just explaining why I put my faith in the conclusion drawn from the difference in velocity apparent from that ammo. Time to do some load development again! Another excuse to head to the range! Thanks to all for your advice and information.