The Tape Test
 

As discussed in this thread http://forum.lugerforum.com/showthread.php?t=37272
a procedure called the "tape test" can be helpful in assessing Luger function.

Objective is to see if the rear of the toggle is striking the frame on recoil, and if yes how hard.

Procedure that I use:
1. Load the pistol with three rounds, to accommodate variations in load strength (I use commercial loads).
2. Chamber a round and put the pistol on "safe". Apply tape to the rear of the receiver. Acquire target and move the safety to fire position. As Dwight points out in the other thread, this sequence is needed to make sure the tape is not touched when chambering the first round.
3. Fire the pistol and check for indentations.

Toggle #53 is 9mm 1938 Mauser, Winchester White Box 115gr. ammo. I view the strike mark on this frame/tape as a benchmark, as the strength of the recoil spring was carefully calibrated. Originally, the toggle was not striking the frame and the pistol was not holding open on last round. I removed 1/2 coil from the mainspring and re-tested. I continued this sequence until I began getting strike marks (hold open then operated correctly as well). As I recall I had to remove 1 1/2 coils to achieve proper operation.

Toggle #94 is a Model 1906, using Prvi Partisan 93gr. ammo. I view the tape mark as acceptably light. Using Fiocchi 93gr. ammo, there was no tape strike and the pistol did not hold open on last round. So, the tape test showed which brand of ammo this Luger prefers and why.

I find the major value of the tape test is determining if any strike at all is occurring. So far, I've not observed a tape indentation that seems "too strong"; however I'm not sure exactly what that would look like.

A couple more to round out the shooter stable.

Toggle #11 is a '42 byf Mauser using WWB 115gr. Toggle #19 is a Model 1900 using Fiocchi 93 Gr. Lighter weight tape used in both these tests than in the previous post (these were taken on a different date, using what I had on hand).

I view the '42 byf strike as acceptably light.

The Model 1900 strike is also acceptably light. Often I find Fiocchi 93gr. .30 Luger ammo does not seem to be powerful enough to produce a tape strike. In this Luger it is. I view that as valuable information, as I prefer to use the lightest ammo possible that will operate the action, so as to reduce stress on the pistol.

I hope others find this test useful. It has been helpful to me in chosing ammo, and fixing failure to hold open and failure to feed problems.

You know that the rear move of the duckbill is also limited in the inside by the stiker hitting the inner vertical surface of the frame, right?

I have only witnessed some blueing loss at the outside. Nothing else.

From time to time people post photos of very hard inside strikes that have damaged the striker guide, rear of the breech bolt or both. In my collection, some frames show clear evidence of the striker guide hitting the frame, others show none.

On my pistols with evidence of striker guide hitting the frame rear, the striker guides are not marked so I'm guessing it occurred in the past.

I frankly do not understand how striker guide impact to the frame relates to or interfaces with the toggle duckbill strike to the frame. I am hoping someone with knowledge will comment.

Both strikes happen at the same time. The spring tension on the striker guide also serves as a buffer.

Edit. Those heavy inside marks could have got there on 3 70% oveload shot tests for all I know.

Interesting. I re-checked my collection after your post. All three military pistols show evidence of the striker guide hitting the frame, my four commercial .30 Luger examples show no such evidence.

Good write up and pictures.

The tape test is informative, but observing if the toggle locks open or not is simpler, but it does not ID a really strong strike.

I have used the tape test on one pistol that essentially "tore up" the tape- needless to say I changed the mainspring. But that one also "felt" like the spring was weak.

Our friend Gerard Henrotin discusses the internal signs of wear quite well in his e-book Luger Function.

4 Scale, I was comparing your pictures with mine and honestly I cannot see where your tape is touched. On mine,
http://forum.lugerforum.com/attachme...1&d=1500258372http://forum.lugerforum.com/attachme...1&d=1500258861
I can see the shape (better seen without flash?) and if I run my finger over it, I can feel a bit of an indentation on the tape where the bottom of the "duckbill" touched said tape (green). It is barely there and does not go the entire width of the dukbill but there it is nevertheless.

So am I not seeing something I should in your picture?

Use the common white/beige masking tape, clear tape is thinner and harder to see.

Would duct tape be a good stand-in for masking tape?

Is there a correlation intensity and use? by 1914 DWM artillery definitly to a beating compaired to my 08 commercial.

Its adhesive is nastier than masking tape's, you may need to use a solvent to remove residue. These days, masking tape is designed to peel right off. Duck tape is spongy, with a fabric layer and a wad of adhesive, so impressions in it may not be as clear or informative. Anything, in a pinch...

Just remember the "tape test" is not scientific- it will only give you an indication of the action of your particular pistol. If the toggle "cuts" through the tape, you may have a weak mainspring(or an ill fitted rear toggle, or over pressure ammo, or ....)- that is just about all the tape test will tell you. JMHO.

Update: I finally got some painter's tape and shot it today. From the pictures, weak spring or good to go?

IMO looks fine/GTG.

It's good to go.

See no problem there.