Initial load development w/MVP Varmint 5.56

[benchracer]

I finally started load development with my Mossberg MVP Varmint in 5.56 NATO. I will be working with 53 VMAX, Hornady 68 BTHP, 69 SMK, Hornady 75 BTHP, and Hornady 75 AMAX, using CFE 223 and IMR 8208 XBR.

I have completed seating depth tests for the 69 SMK, Hornady 75 BTHP, and 75 AMAX. Results are pictured below. Seating depth tests for the 53 VMAX and 68 BTHP, along with powder charge workups for all five bullets and CFE 223 soon to come...

 

[benchracer]

Here are two ten-shot groups using the Hornady 68 BTHP and 69 SMK's loaded with CFE 223 and seated to mag length. These were some of the first rounds fired, with no load development.

 

[benchracer]

I am having issues with pierced primers, absent other pressure signs, during my load workups. I suspect there may be a firing pin protrusion issue, or perhaps, I may need to change primers. Development is at a halt until I get this sorted out. Here is something I found that may be relevant:

Primers And Pressure


Will have to do some testing and measuring to see what the fix is...

 

[benchracer]

Here are two ten-shot groups using the Hornady 68 BTHP and 69 SMK's loaded with CFE 223 and seated to mag length. These were some of the first rounds fired, with no load development.

68 BTHP

AVG 2701
ES 184
SD 55


69 SMK

AVG 2755
ES 68
SD 17


I have attached screen shots of the QL predictions for both loads. Relevant OBT-predicted nodes fall at 1.030ms, 1.120ms, and 1.250ms.

 

[benchracer]

I have completed seating depth tests for the 69 SMK, Hornady 75 BTHP, and 75 AMAX. Results are pictured below.

Again, the QL predictions for each bullet at the preferred seating depth are attached. Relevant OBT nodes are predicted at 1.030ms, 1.120ms, and 1.250ms. All nodes are generally considered to be +/- .020ms.

Based on OBT predictions, the 75 AMAX needs to be backed down slightly from the charge used in the seating depth test.

The 75 BTHP seating depth test, with the powder charge used, fell right on the uppermost predicted node. This may well prove to be the final load for this bullet, pending velocity and accuracy testing.

Though not noted in the photo, the powder charge for the 69 SMK seating depth test was 27.3 grains, which was right in a predicted node.

I will be re-visiting this testing (possibly with magnum primers) once I have the primer-piercing issue worked out.

 

[Jud96]

Again, the QL predictions for each bullet at the preferred seating depth are attached. Relevant OBT nodes are predicted at 1.030ms, 1.120ms, and 1.250ms. All nodes are generally considered to be +/- .020ms.

Based on OBT predictions, the 75 AMAX needs to be backed down slightly from the charge used in the seating depth test.

The 75 BTHP seating depth test, with the powder charge used, fell right on the uppermost predicted node. This may well prove to be the final load for this bullet, pending velocity and accuracy testing.

Though not noted in the photo, the powder charge for the 69 SMK seating depth test was 27.3 grains, which was right in a predicted node.

I will be re-visiting this testing (possibly with magnum primers) once I have the primer-piercing issue worked out.

Try some Wolf primers or CCI small rifle military primers. They have a hard cup and are designed to run in 5.56 ARs. Military ammo has tough primers so it sounds like your rifle has a firing pin designed to reliably set off military shells and it is tearing through softer cupped primers. What primers are you currently using? Also, magnum primers are not needed in a .223/5.56

 

[benchracer]

Try some Wolf primers or CCI small rifle military primers. They have a hard cup and are designed to run in 5.56 ARs. Military ammo has tough primers so it sounds like your rifle has a firing pin designed to reliably set off military shells and it is tearing through softer cupped primers. What primers are you currently using? Also, magnum primers are not needed in a .223/5.56

I am using standard CCI small rifle primers, not known to be soft. Read the link I posted, then you will understand why I am going to magnum primers.

I suspect the issue is caused, in part, by excessive firing pin protrusion. I am going to try to find out what the factory spec is.

 

[benchracer]

I made the switch to magnum primers and the problem with pierced primers went away. I didn't pursue firing pin protrusion specs with Mossberg.

I also shifted gears and made a fresh start with load development. Rather than load for optimum seating depth, I am loading all bullets tested to mag length and doing a powder charge workup only. I am doing this to allow mag feeding from any of my AR mags and to allow me to use the loads I work up in other rifles.

Here is the load workup for the 69 SMK and CFE 223:

 

[benchracer]

Here is the load work I did with the Hornady 68 BTHP and CFE 223:

 

[benchracer]

Results with the Hornady 75 BTHP and RL-17:

 

[benchracer]

Results with the Hornady 75 BTHP and Superformance:

 

[benchracer]

I have had excellent results with 53 VMAX's and CFE 223, but no pics of the load development process with them. I will try to get some pics of groups fired at 200 and 300 yards the next time I am out, probably after Labor Day...

Load workup is in progress with the new 69 TMK's and CFE 223. Will post pics when I have something.

I am also working with 75 AMAX's loaded to 2.455 COAL using CFE 223, RL-17, and Superformance.

I will be gathering chrono data for my final loads with the 53 VMAX, 68 BTHP, 69 SMK, and 75 BTHP tomorrow. Will post that data when I have it.

 

[benchracer]

I loaded 10 rounds @ 27.7 grains of CFE 223, firing 5 rounds across my Magnetospeed chrono from my MVP Varmint and 5 rounds from a friend's MVP Varmint. Here are the results from each rifle:

Min 3101
Max 3176
Avg 3133
ES 75
SD 28



Min 3092
Max 3140
Avg 3120
ES 48
SD 19

I made the switch to magnum primers and the problem with pierced primers went away. I didn't pursue firing pin protrusion specs with Mossberg.

I also shifted gears and made a fresh start with load development. Rather than load for optimum seating depth, I am loading all bullets tested to mag length and doing a powder charge workup only. I am doing this to allow mag feeding from any of my AR mags and to allow me to use the loads I work up in other rifles.

Here is the load workup for the 69 SMK and CFE 223:

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[benchracer]

Here is the load work I did with the Hornady 68 BTHP and CFE 223:

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Chrono results with the 68 BTHP loaded @ 26.8 CFE 223:

Min 3012
Max 3117
Avg 3071
ES 105
SD 39

Min 3061
Max 3092
Avg 3073
ES 31
SD 15