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Reticle jump when dry firing

Kevin1990

This has been hashed out in other threads, but they are somewhat old.

I have a defiance tenacity action. Waiting on a few other parts for a 30br build. I have a plain mcmillian kestros for this new build. Anxious to try it out, So I figured id slap my defiance action with my 26" bull barrel in 6br in it. Has a trigger tech special trigger in it. Also, has an Arken sh4 scope.


So now to my problem. When I dry fire off a front rest and rear bag, the reticle which has a center dot will move either to the right or up. I'm 50 yards away from a 1/4" bullseye. When I pull the trigger the reticle will move anywhere between 1/16"-1/4"

Remedies ive tried.
Tried a spent case and that helped a little.
Tried "fluffing up" the front bag.
Scope is verified good to go. Doing the same thing with other scopes.


Any ideas or suggestions? Is this just somthing that cant be avoided, or is it somthing with my form?
 
I have experienced the same issue. What I found with mine was usually associated with the rear bag. It was either my butt stock wasn’t settled in the bag fully or the sand in the rear bag had fluffed up during transport and needed packed on the bench.
 
I think our sandbag supported disciplines want the rifle to require shot to shot readjustment, and operate less “ideally” than is mechanically possible. The rules seem to contemplate that depressible sandbags will function differently than rail guns, seeking to preserve that involvement and the skill of correcting the point of aim.

I have a tenacity on a .243 Fclass gun and admire how it functions. Kestros is also a known quantity.

There is a way to determine if the gun’s mounts or scope has a problem, which is to dry fire it gently clamped to a solid surface or placed in a padded vice, and compare movement to what you are seeing with sandbag support front and rear.
 
@davidjoe great advice. I will clamp it in my padded vise, and see if the results differ.

@Brx6 its all happening so quickly. Its definetly happening when the hammer is dropping or when its striking the firing pin. The trigger is set to,as low as it will go (16 is.) And I can put like 15oz of prssure on it and everything stays as it should. As soon as it breaks. That's when im having issues.
 
gmorris said:
Could be action timing of bolt vs firing pin
Click to expand...
Very well could be. I bought the action, slapped a prefit on it, with the trigger tech special, and put it in a KRG bravo. Thats about the extent of my gunsmithing skills in regards to bolt actions.

I read in previous threads that this could be a firing pin spring issue as well? However I feel like i remeber this happening with my tikka before I sold it, thats why I was wondering if it was a possible form issue. As of late, and I dont know why, but I tend to blame myself before my equiptment.
 
A quarter to half MOA movement is a LOT.

At 100 yards, looking at a .8" bullseye, I see no perceptible movement in the reticle at 20X at trigger release. [This is slung up in prone - but thinking that shouldn't make any difference]

It will be interesting to see the results of dry firing in the vise.
 
Kevin1990 said:
100 percent Agreed! I guess I'm more worried about it possibly effecting my groups, more so than functionality.
Click to expand...
I do a lot of dry firing, especially in the winter and for many years have notice the horizontal reticle jump the moment the fire pin is struck on several different rifle / scope combos however all group consistently and hold POI.

I do not have a clue what is causing this or if it merely and illusion created by the energy of the firing pin release causing the rifle to vibrate, etc. However, as long as it doesn't cause a performance issue, I really do not care and just ignore it.
 
Year ago, I looked at this using my 6PPC built with a Stiller Viper action. One thing that was interesting was that, comparing it with two different rear bags, one was a lot better for reticle jump than the other.

When a rifle actually fires the firing pin is stopped by the primer, which is a major difference from dry firing with an empty chamber or even a fired case with a previously fired primer, where the amount of cushion has been reduced by the primer being fired.

I have not done it, but you might try this. Try it with a primed case, with very close to tight fit in the chamber. Let us know what you see. The other thing that can cause motion is how the trigger is pulled and its weight.

In benchrest two ounce triggers are the rule. For other shooting they would not be appropriate. In those cases the impact on the trigger's over travel stop would undoubtedly be a contributing factor.

Another possible issue is how you pull the trigger. A friend discovered an issue with this by dry firing and was able to reduce reticle motion, and the size of his groups by modifying how he pulls the trigger so that it is more correct.

One more thing that you may try, that may not be practical for your type of shooting and level of recoil, but which would be interesting for testing, would be to pinch the trigger with your thumb on the back of the trigger guard. Good luck with your research.
 
So a little update. I did what @davidjoe said and I actually used a ratchet strap to secure the rifle down to the table. There was no movement. I took the rifle back out and put it back in the front rest. I took my rear bag and pinched the ears. The reticle that I have is a center dot. I aimed at a 1/8 inch dot at 50 yards. The reticle covers up 95 percent of the dot. When I squeeze the bag, I get virtually no movement and the dot stays in the circle. Heres a link the rear bag I'm using.
I want to try a a flattop DR bag from protecktor.


@BoydAllen always great info. Thank you! My 30br will be strictly off a bench, so I will try a different rear bag. I'll try with a primer in one and let you know how it goes.

My trigger is set at 16oz. I was going to switch to a trigger tech diamond at 4oz. The trigger pull In the TT special is heavy for my liking, but I figured if i can't get it right with the trigger then i shouldnt move to a better one? Rookie question, but do the trigger tech triggers hammers drop harder than a Jewell or, BnA, etc?


protektormodel.com

#13B Rabbit Ear Rear Bag with Hard Bottom

The famous #13B Rabbit Ear Rear Bag is 3-3/4" H to the bottom of the ears then tapers downward slightly towards the eagle. Includes a single hard bottom for added stability. It also has reinforced sides to keep the bag from bulging over time. Each ear is 2-5/8" tall and has a single stitch sewed...
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